I respectfully dissent.

I disagree with the posture in which the majority have placed the matter on appeal, which is the predicate for their lengthy discussion on the question of reemployment rights under Education Code sections 87744 and *93087745; it is my opinion that the substance of this case is dealt with by Education Code section 87743 which relates to layoff, not reemployment.

Additionally, the majority opinion gives no more than lip service to the trial court’s determination that plaintiffs’ action was barred by laches. In their conclusion on that question, I believe they are wrong. I view that question as pivotal to the proper disposition of the matter.

In order to adequately state my dissenting decision, I set forth the following factual and legal analysis to support my belief that the judgment should be affirmed.

In 1977, the Educational Employment Relations Board (now the Public Employment Relations Board [see Gov. Code, § 3541]) directed that the Shasta-Tehama-Trinity Joint Community College District (District) part-time (temporary) certificated instructors be included in the same bargaining unit with the District’s full-time (permanent) certificated instructors.

In 1978, the Shasta College Faculty Association (Association), the exclusive bargaining agent for the unit, negotiated a master contract agreement with the District on behalf of all certificated instructors. A high priority item in those negotiations was job security for part-time instructors. Consequently, eligible part-time instructors were accorded layoff and reemployment rights in part-time (evening) courses on the basis of seniority in the part-time service.1 Those contract provisions resulted in the District’s *931establishing, at the Association’s insistence, a separate part-time seniority list to govern assignments into the evening classes.

In 1982, in the face of financial constraints, the District elected to discontinue or reduce services in several areas of its curriculum, necessitating the layoff of a number of full-time, certificated faculty members, including plaintiffs, for the 1982-1983 school year. On April 21, 1982, pursuant to Education Code sections 87740 and 87743, the affected employees were provided a layoff hearing before an administrative law judge.2 Each of the plaintiffs was represented by counsel at the hearing. At the hearing plaintiffs did not challenge the use of dual seniority lists for full-time and part-time instructors, nor did they assert any right to displace, or “bump,” any part-time instructors teaching in areas for which plaintiffs were credentialed and qualified. The administrative law judge found cause for not reemploying plaintiffs because of discontinuance or reduction of certain services, and he further found that “[n]o certificated employees with less seniority are being retained for service which any [laid-off employee] is certificated and competent to render.”

On May 5, 1982, the District’s governing board adopted the administrative law judge’s decision. That same month, the fall 1982 teaching schedule was published and distributed. The schedule included evening classes to be taught by part-time instructors who were being reemployed for the following school year. Following receipt of that schedule, plaintiffs did not request a reconsideration of the layoff decision (see Gov. Code, § 11521), nor did they file a petition for a writ of administrative mandamus challenging the decision (see Gov. Code, § 11523; Code Civ. Proc., § 1094.5).

On June 11, 1982, by letter to the District, plaintiff Dick Kakuda asked for a position teaching any of 11 evening courses being offered in the fall 1982 semester, or any other courses for which his credential qualified him. His request was not construed by the District to be an assertion of a reemployment right, and the request was apparently denied. Kakuda made no objection at that time.

When the spring 1983 teaching schedule was published, the District again heard no protest from plaintiffs or from the Association.

*932In mid-April 1983, one year after the layoff hearing, the Association filed grievances on plaintiffs’ behalf. The Association challenged the District’s use of dual seniority lists under the master contract, and it requested plaintiffs’ reinstatement with backpay. The District denied the grievances in September 1983, and the Association requested binding arbitration. An arbitration hearing was held January 19, 1984, and a decision adverse to the Association was rendered May 25, 1984.

The individual grievants subsequently filed the instant petition for a writ of mandate seeking reinstatement with backpay. They further petitioned the superior court to vacate the arbitrator’s decision as contrary to public policy and beyond the scope of the arbitrator’s authority.3 Plaintiffs’ position, in essence, was that the Education Code accords them, as full-time (permanent) certificated instructors, layoff and reemployment rights not accorded part-time (temporary) instructors.4 They asserted that their statutory reemployment rights preempt the part-time instructors’ contractual rights to the extent part-time instructors have been employed, beginning with the 1982-*9331983 school year, to teach evening courses for which plaintiffs are credentialed and qualified. Moreover, to the extent the master contract protects part-time instructors at the expense of full-time instructors, it is contrary to public policy and presents a nonarbitrable matter.

The District disagreed with plaintiffs on the merits of the controversy. In addition, the District interposed the defenses of laches and statute of limitations. The District maintained that plaintiffs were asserting nothing more than bumping rights, which should have been advanced at the layoff hearing in April 1982. In reliance on plaintiffs’ apparent acquiescence in the District’s use of dual seniority lists, part-time instructors were reemployed to teach in the evening division for the following school year. Despite their knowledge of the pertinent facts in April or, at the latest, May of 1982, plaintiffs first raised this issue one year later, in April 1983, when they filed their grievances under the master contract. The District argued the delay was unreasonable in the circumstances, and the District was prejudiced by it in that it had previously reemployed and paid the part-time instructors for the evening positions now claimed by plaintiffs. Moreover, under the terms of the master contract, the part-time instructors could not be dismissed without cause, and dismissal of the part-time instructors to accommodate plaintiffs’ demands would potentially cause additional litigation for the District. In addition, the District asserted plaintiffs’ exclusive remedy for any asserted violation of bumping rights was by way of administrative mandamus (Code Civ. Proc., § 1094.5), not ordinary mandamus (Code Civ. Proc., § 1085). Accordingly, plaintiffs’ action is barred by the 30-day limitation period for filing a petition for writ of administrative mandamus. (See Gov. Code, § 11523.)

Following a hearing at which the records of the prior layoff and arbitration hearings, as well as testimony of the District’s superintendent, were received into evidence, the superior court found that, regardless of the merits of plaintiffs’ claim, they unreasonably delayed asserting it, to the District’s detriment.5 The writ petition was denied, as was the petition to vacate the arbitration decision, and judgment was entered for the District accordingly.

“The defense of laches requires unreasonable delay plus either acquiescence in the act about which plaintiff complains or prejudice to the defendant resulting from the delay. ... ‘If because of his delay in seeking his *934remedy, without offering a satisfactory explanation for the delay, a prejudice results to his adversary, he will be precluded from enforcing his demand. It is not so much a question of the lapse of time as it is to determine whether prejudice has resulted. If the delay has caused no material change in statu quo, ante, i.e., no detriment suffered by the party pleading the laches, his plea is in vain.’ ” (Conti v. Board of Civil Service Commissioners (1969) 1 Cal.3d 351, 359-360 [82 Cal.Rptr. 337, 461 P.2d 617], quoting Brown v. State Personnel Board (1941) 43 Cal.App.2d 70, 79 [110 P.2d 497], fns. omitted.)

In an action by a discharged public employee for reinstatement with backpay, the defense of laches may be established by a showing that the position for which reinstatement is sought has been filled by another; the resulting double payment by the employer would constitute prejudice. (Conti, supra, 1 Cal.3d at p. 360; Vernon Fire Fighters Assn. v. City of Vernon (1986) 178 Cal.App.3d 710, 726 [223 Cal.Rptr. 871].) This type of prejudice is aggravated when the position sought by the discharged employee has since been filled by one who may not be terminated except for cause. Thus, in Kimberlin v. L. A. City High School Dist. (1953) 115 Cal.App.2d 459 [252 P.2d 344] (disapproved on another point in Conti, supra, at p. 362), a teacher sought reinstatement and backpay about one year after his discharge. In the interim, the school district had hired and paid another teacher, on a written contract basis, for the position demanded by the plaintiff. This was sufficient to sustain the school district’s laches defense: “This notwithstanding the fact that at the trial, appellant, through his counsel, offered to waive his right to receive compensation for the period prior to judgment should the court order his reinstatement. Without undertaking to determine the effectiveness of such purported waiver, the fact remains that another had been appointed to the position formerly held by appellant, whose employment may not be terminated except for cause. [Citation.] Thus the respondent district would be prejudiced if appellant were now reinstated by reason of the financial burden incident to the addition of another employee.” (115 Cal.App.2d at p.465.)

“Ordinarily laches is a question of fact. [Citation.] Whether laches has occurred in a particular case presents a question primarily for the trial court, and an appellate court will not interfere with a trial court’s discretion in this respect unless it is obvious that manifest injustice has been done or unless its conclusions do not find substantial support in the evidence. [Citation.]” (Chang v. City of Palos Verdes Estates (1979) 98 Cal.App.3d 557, 563 [159 Cal.Rptr. 630]; see Vernon Fire Fighters Assn. v. City of Vernon, supra, 178 Cal.App.3d at pp. 718-719 [substantial evidence standard of review].) I review the record accordingly.

*935Initially, in order to place this matter in what I believe is its proper perspective, I observe what this case is not about. Regardless of the label plaintiffs and my colleagues in the majority opinion attach to it, this case is not about reemployment rights under Education Code sections 87744 and 87745. Plaintiffs were laid off under Education Code section 87743 after the District decided to reduce or discontinue particular services that plaintiffs had theretofore been employed to render. For instructors so laid off, Education Code sections 87744 and 87745 provide a preferred right to reappointment if, within the specified time periods, “the discontinued service is reestablished.”6 I fail to discern any evidence in this case that that predicate to plaintiffs’ preferred right to reappointment had occurred. Indeed, I believe the evidence from the District is uncontroverted, that the discontinued services for which plaintiffs were laid off had not been reestablished. Under those circumstances, Education Code sections 87744 and 87745 do not come into play. Reduced to its essence, plaintiffs’ complaint is that assertedly less senior, part-time instructors were retained by the District to render services which plaintiffs were certificated and competent to render. This places plaintiffs’ claim within the purview of Education Code section 87743, which relates to layoff, not reemployment, rights.

The record discloses that plaintiffs, aware of the District’s use of dual seniority lists for full-time and part-time instructors, failed to assert at their layoff hearing any right to bump part-time instructors who were being retained.7 Within 30 days of the District’s adoption of the administrative decision finding cause for plaintiffs’ layoff, the District published and distributed its teaching assignments for the 1982-1983 school year. Assuming the publication of these assignments was plaintiffs’ first notice that part-time *936instructors were being retained to teach evening classes for which plaintiffs were credentialed and qualified, plaintiffs did not, despite their right to do so, request a reconsideration of the layoff decision. Nor did they petition the superior court for a writ of administrative mandamus. Plaintiffs’ first indication to the District that they considered the use of dual seniority lists improper in making teaching assignments came one year after the layoff hearing. In the interim, and in reliance on plaintiffs’ apparent concurrence in the District’s interpretation of the master contract, the District retained and paid part-time instructors to teach the classes now claimed, with back-pay, by plaintiffs. Moreover, by the terms of the master contract, the retained part-time instructors were not subject to dismissal except for cause.8 Finally, plaintiffs have simply offered no satisfactory explanation for their delay in asserting the invalidity of the dual seniority lists.9 The record amply supports the superior court’s finding that plaintiffs unreasonably delayed asserting their claim, acquiescing for one year in the District’s interpretation of the master contract, to the District’s prejudice. Perceiving no manifest injustice in the circumstances, I would conclude the court did not abuse its discretion in sustaining the District’s laches defense.

In any event, I am persuaded by the District’s argument that, because plaintiffs’ claim is essentially an assertion of bumping rights (in the guise of an assertion of reemployment rights), their exclusive remedy, assuming the assertion has merit, was through the administrative layoff procedure. Having failed to request reconsideration of the administrative decision or to seek judicial review by petition for writ of administrative mandamus within the 30-day limitation period (see Gov. Code, §§ 11521, 11523), plaintiffs are barred from asserting their claim in this proceeding. (See Temescal Water *937Co. v. Dept. Public Works (1955) 44 Cal.2d 90, 106 [280 P.2d 1]; Compton v. Board of Trustees (1975) 49 Cal.App.3d 150, 154, 159 [122 Cal.Rptr. 493].) Moreover, to the extent plaintiffs argue the evidence giving rise to their claim did not arise until after the administrative decision—i.e., the subsequent publication and distribution of the 1982-1983 teaching assignments— the fact remains that this evidence came to light within the 30-day period for administrative reconsideration of the decision. By failing to avail themselves of that opportunity for reconsideration, plaintiffs have simply waived judicial review of the matter for their lack of reasonable diligence. (Cf. Schoenen v. Board of Medical Exrs. (1966) 245 Cal.App.2d 909, 915 [54 Cal.Rptr. 364].)

The parties raise a number of other procedural points, as well as renewing their arguments made below on the merits of plaintiffs’ claim; because of my conclusion that laches was properly invoked, I have not addressed those arguments.

I would affirm the judgment.

Opinion

This mandamus action (Code Civ. Proc., § 1085) involves the reemployment rights of regular (tenured) and contract (probationary)1 community college teachers, whose jobs were terminated by layoff, to positions created and assigned to temporary, part-time teachers after the layoff. It arises following the 1982 layoff of appellants, regular and contract employees. Following the layoff, the Shasta-Tehama-Trinity Joint Community College District (District) hired temporary, part-time instructors (apparently temporary employees who previously taught evening classes) to teach evening classes in the District.2 Appellants were not offered these positions. The pivotal issue is whether appellants have a preferred right to reappointment to teach such classes.

Appellants contend that the statutes which provide for the reappointment of teachers whose jobs were terminated by layoff (Ed. Code, §§ 87744, 87745) obligated the District to offer them temporary positions created within the periods (39 and 24 months respectively) to which such reemployment rights extend. The District claims that appellants have no right to *913those positions because they are evening positions to be filled only by the part-time employees, a consequence it says stems from a collective bargaining agreement between the District and the Shasta College Faculty Association (Association). The District also contends that appellants’ delay in challenging the hiring of the temporary employees precludes them from obtaining any relief.

We agree with the appellants that the Education Code provides them with a preferred right to reappointment to perform services which they are certificated and competent to render in any position held by a temporary employee which is created after their layoff, i.e., to positions which the District has created for assignment to temporary employees. We further agree with appellants that the trial court’s finding of laches in initiating the claim was erroneous as to temporary positions created thereafter.

Facts and Procedural Background

We begin with a chronology of events leading to this appeal. Appellants are all regular (permanent) or contract (probationary) employees.3 (Ed. Code, §§ 87604, 87601, 87609.)4They are entitled to notice and a hearing prior to termination of their employments. (§ 87740; Balen v. Peralta Junior College District, supra, 11 Cal.3d at p. 826.) In March 1982 appellants were notified that they were to be laid off pursuant to section 87743, the provision governing the layoff of tenured and probationary employees because of a “reduction in attendance” or a “reduction or discontinuance of a particular kind of service.” (§ 87743.)5 The layoff notices included a list of the positions to be reduced in the various departments. It stated that the specified services to be reduced or discontinued were the full-time equivalent of 18.78 teaching, counseling, and library positions. No distinction was made between daytime classes and evening classes.

*914Section 87743 provides that whenever it becomes necessary by reason of either of the specified conditions “to decrease the number of tenured employees in the district, the governing board may terminate the services of not more than a corresponding percentage of the employees of the district, tenured as well as probationary . . . .” The section further provides that “the services of no tenured employee may be terminated under this section while any probationary employee, or any other employee with less seniority, is retained to render a service . . . [for which] the tenured employee possesses the minimum qualifications . . . and is competent to serve . . . .” (Italics added.) This statute contemplates layoff proceedings for only tenured and contract employees. It specifically provides that in the event a “tenured or probationary employee” is not given the statutory notice and hearing right, “he or she shall be deemed reemployed for the ensuing school year.” (Ibid.) The exclusive applicability of this section to tenured and probationary employees is consistent with the scheme provided in the Education Code relating to temporary employees, i.e., they are dismissable at will (§ 87742) and they are hired for a limited (and designated) duration. (§ 87477;6 see also Peralta Federation of Teachers v. Peralta Community College District (1979) 24 Cal.3d 369, 380 [155 Cal.Rptr. 679, 595 P.2d 113].)

The layoff hearing in this case was held on April 21, 1982, before an administrative law judge with the Office of Administrative Hearings. Appellants were represented at that hearing by the Shasta College Faculty Association (Association), their exclusive bargaining agent. At the commencement of the hearing, a conversation ensued between the hearing officer (CEO), the Association, and the District regarding the propriety of “accusations” (i.e., layoff notices) which were sent to temporary (part-time) employees. The parties agreed that the temporary employees were not entitled to a hearing before the governing board. The District consequently withdrew the accusations as to those employees.

A seniority list containing the names of the District’s tenured and contract employees was presented as an exhibit by the District. That exhibit served as the focus of the questioning relating to the propriety of certain layoffs. Testifying at the hearing, the District’s chief executive officer, Kenneth Cerreta, related the number of positions in the various departments *915that were to be reduced; no distinction between day and evening classes was made. Cerreta then testified about steps taken to verify the accuracy of the seniority list. Upon the questioning of the District’s counsel, the CEO gave a detailed list of the identity of the employees (and a description of their positions) on the seniority list that the District intended to “protect or skip over,” i.e., employees with seniority numbers lower than those of appellants who were being retained because they provided services for which appellants were not qualified or credentialed to teach. The only employees the District claimed to be “skipping” over were tenured and contract employees; no names of temporary employees were mentioned.

The Association challenged the reasons for reduction in certain services, the categorization of some instructors (e.g., as a “Composition and Remediation” instructor as opposed to an “English” instructor), an allegation of capriciousness as to a particular layoff and an assertion by one instructor of a right to “bump” a less senior full-time instructor who was being retained. One instructor expressly waived her right to bump a less senior full-time instructor.

The decision of the administrative law judge, adopted by the governing Board, stated that cause had been established “for not reemploying 17.33 FTE certificated employees . . . under Section 87743 . . . because of discontinuance or reduction in particular kinds of service . . . .”7 It included a list of the tenured and contract employees to be laid off and the full-time equivalent figures for each of their services; the total equaled 17.33 full-time equivalent certificated employees. The decision included the finding that “[n]o certificated employees with less seniority are being retained for service which any [laid-off employee] is certificated and competent to render.” It further stated that the accusations against the temporary employees “should be dismissed” and it specifically deemed one employee (as to whom there was a dispute as to her status) “a temporary employee without any employment rights under Section 87743.”

On June 11, 1982, by letter to the District, petitioner Dick Kakuda asked for a position teaching any of 11 evening courses to be offered in the fall 1982 semester. His request was denied.

In mid-April 1983, almost one year after the layoff hearing, the Association filed grievances on appellants’ behalf. It claimed a right by appellants to positions in the evening classes offered in 1982-1983 and filled by temporary instructors. After the grievances were denied by the District, an *916arbitration hearing was scheduled. At the hearing, the Association expressed its objection to the arbitrability of the issue. Following the hearing, the arbitrator concluded that, pursuant to the 1981-1984 collective bargaining agreement between the District and the Association, the tenured and contract employees do not “have a right ... to bump an evening instructor” and that the District did not violate the agreement by failing to assign appellants “who were day-time instructors, on layoff status, employment as evening instructors.” In reaching this conclusion, the arbitrator relied in part on the fact that the agreement provides for the creation of a separate seniority list for temporary employees. The arbitrator also construed the agreement as vesting in the District the right to assign full-time instructors to an evening class; he concluded that the full-time instructors did “not have the right, unilaterally, to exercise his/her . . . seniority to bump a part-time (temporary) employee.” (See fn. 9, infra.)

Appellants subsequently filed this mandamus petition (Code Civ. Proc., § 1085) and petition to vacate the arbitration award in superior court. In the mandamus action, they sought an order obligating the District to accord them their statutory rights of rehire pursuant to sections 87744 and 87745. Those sections give laid-off tenured (§ 87744) and contract (§ 87745) employees a preferred right to reappointment to any position which they are competent and certificated to render for respectively 39 months and 24 months, “if the number of employees is increased or the discontinued service is reestablished . . . .” (§§ 87744, 87745.) Section 87744 further provides that “no contract or other employee with less seniority shall be employed to render a service which the employee is certificated and competent to render” while section 87745 provides that “no contract or temporary employee with less seniority shall be employed to render a service which such employee is certificated and competent to render . . . .” Both sections also give a preferred right to the laid-off employees to “be offered prior opportunity for temporary service during the absence of any other employee who has been granted a leave of absence or who is temporarily absent from duty.” (§§ 87744, subd. (d); 87745, subd. (c).) Section 87744 additionally allows a tenured employee to waive the right to reappointment for up to one school year.

Appellants allege in their petition that commencing with the 1982-1983 school year and each succeeding year thereáfter the “District has re-established and continued the services which were discontinued in the 1982 Layoff Proceeding” and beginning in 1982-1983 the District has made appointments for evening classes “solely from the seniority list maintained for temporary . . . employees . . . .”

At the mandamus hearing in the superior court, the parties agreed to bifurcate the issues before the court. The parties stipulated that the first *917issue before the court was “Whether the District was obligated by virtue of Sections 87744 and 87745 of the Education Code [statutes providing rights of rehire to permanent (tenured) and contract (probationary) teachers following layoff] to offer to the Petitioners or any of them who were laid off in the 1982 reduction in force proceeding pursuant to the provisions of Section 8774[3] of the Education Code . . . Positions in the so-called evening program as that term is used in the arbitration hearing for which Petitioners were credentialed and competent, for any school year starting with the 1982/1983 school year all the way up to date . . . (Italics added.) The parties agreed to reserve for the second part of trial the issues of the “identity ... of each position occupied by some part-time temporary employee commencing with July 1, 1982, all the way to today for which . . . any of the Petitioners had a right to claim rehire rights. . . . And the amount of damages and the existence of damages, if any, for each of Petitioners and the amount and scope of any other relief for each of Petitioners.”

This stipulation notwithstanding, in their trial brief appellants addressed the District’s defense of laches. The District had alleged in its answer to the petition that appellants had unduly delayed in their action seeking reinstatement and that such delay was prejudicial. The District had also alleged that appellants had failed to exhaust their administrative remedies by failing to assert their right to the evening classes at the layoff hearing.

The stipulated issue presented to the court essentially was whether the laid-off tenured and contract teachers had a statutory right to be offered the positions ultimately occupied by part-time temporary teachers beginning in the 1982/1983 school year, i.e., the session immediately after the layoff. The District’s position was that it had no obligation to offer the laid off tenured teachers the evening positions because of provisions in the 1981-1984 master contract agreement. Its claim was that, as a consequence of the Association negotiating provisions giving greater benefits to the part-time instructors than given by statute and providing for the creation of a seniority list for the part-time temporary employees, the tenured teachers had no right to the evening classes.

The trial court never resolved the legal question of appellants’ rights under the statutes. In its statement of decision, it chronicled the events leading up to the master contract, the events at the layoff hearing, and the subsequent events leading to this lawsuit. The court then concluded that the defenses of laches and estoppel were available to the District. As to the estoppel defense, the court asserted that (1) the Association “was responsible for the conditions which led to the disputed interpretation of the Master Contract and its relationship to the [appellants’ statutory] rights,” and (2) the appellants were aware of the “District’s interpretation of their rights in *918the contract, perhaps as early as April 1982, but most certainly by May 1982, but failed to take “any formal action upon which the District could have legally acted until April 1983.” The court stated that “[djuring said period the District had expended and committed the expenditure of a considerable amount of funds in reasonable reliance on the Petitioners’ conduct.”

As to the laches determination, the court relied for the prejudice requirement on appellants’ delay in bringing this action until after temporary employees were hired and paid for a full year.

The court asserted that appellants were estopped not only from asserting any rights relating to the 1982-1983 school year (i.e., the school year following the layoff and preceding the filing of this action) but also from asserting any rights under sections 87744 and 87745 relating to the 1982 layoff (i.e., any rights in the positions for the school year beginning after this action was filed.) The court rejected the claim that, even if appellants had been derelict in asserting their rights to the evening positions in 1982, they were entitled to those positions the semester following the filing of their grievance. Although the court acknowledged that the appellants’ position on this issue “has some merit” it reasoned that because the temporary employees had been paid for the 1982-1983 school year and because appellants had not waived any backpay as to that year the grant of any rehire rights to the appellants would be to the District’s prejudice.

Appellants claim on appeal8 that the District failed to comply with the rehire provisions of sections 87744 and 87745.9 Their position essentially is that the statutory prerequisites to their reappointment priorities are met (i.e., the number of employees is increased or the discontinued service is reestablished) whenever an evening class (generally taught by part-time, temporary teachers) is offered in a new semester because temporary teachers are “uniformly dismissed” at the end of each school year. The District retorts that tenured and contract employees’ rehire rights provided by those sections do not apply to classes taught in the evenings. The District’s claim *919essentially is that there are two distinct and separate “services of certificated employment in community colleges, the daytime program and the evening program” and that instructors in the daytime program have no rights in the evening classes. The District argues that it “was not obligated to offer the evening positions to Appellants because the Education Code does not create the rights they allege.”

Appellants also challenge on appeal the trial court’s laches and estoppel determinations. They argue that because the District did not raise an estoppel defense below, the trial court erred in making a finding on that issue. They further argue that their claims are not barred by laches because the District has failed to show prejudice arising from their assertion of their rights.

Discussion

I

We first consider the question posed to the trial court, i.e., appellants’ statutory rights to be offered the contested positions. As we stated above, the Education Code requires compliance with specified procedures before a tenured or contract employee can be laid off because of a reduction in services. The layoff statute gives priority to tenured employees over contract employees (see § 87743) and priority based on seniority. The layoff statute makes no mention of temporary employees. The rehire statutes, sections 87744 and 87745, which have significance only after a layoff pursuant to section 87743, provide for the order of rehiring the laid-off tenured and contract employees when “the number of employees is increased or the discontinued service is reestablished . . . .” If a laid-off tenured employee is certificated and competent to render a service, he or she has a preferred right to reappointment for a period of 39 months over a “contract or other employee with less seniority . . . .” (§ 87744, subd. (a).) A laid-off contract employee has a preferred right to reappointment for a period of 24 months “subject to the prior rights to reappointment by all [tenured] employees as set forth in Section 87744” over any “contract or temporary employee with less seniority.” (§ 87745, subd. (a).) Both sections further provide that the preferred right to reappointment applies even in the absence of an increase in employees or reestablishment of a discontinued service to a position of “temporary service during the absence of any other employee who has been granted a leave of absence or who is temporarily absent from duty.”10 (§§ 87744, subd. (d); 87745, subd. (c).)

*920These statutes create a hierarchy of rights. Laid-off tenured employees have preferred reappointment rights over contract employees who have priority over temporary employees. Additionally, within each of those categories, seniority has priority.

At the time the predecessor statutes to the current layoff and rehire statutes were enacted (see Stats. 1959, ch. 2, p.949; former §§ 13447, 13448, 13448.5), temporary employees were those employed to teach “temporary” classes of up to three or four months duration. (Stats. 1959, ch. 2, § 13337, p. 937.) “Substitute” employees were those filling positions of “regularly employed persons absent from service.” (Stats. 1959, ch. 2, § 13336, p. 937.) Both temporary and substitute employees were dismissable “at the pleasure of the board.” (Stats. 1959, ch. 2, §§ 13445, 13446, p.949.)

In 1967, the Legislature included within the definition of “temporary employee” any person “employed to teach adult or community college classes for not more than 60 percent of the hours per week considered a full-time assignment for regular employees having comparable duties .... [They] shall not become a contract employee . . . .” (§ 87482.5, subd. (a); see former § 13337.5.) Thus, part-time employees were deemed to be temporary employees with the same job insecurity. In Peralta Federation of Teachers v. Peralta Community College Dist., supra, 24 Cal.3d at p. 380, the Supreme Court asserted that the 1967 legislation adding the less-than-60percent employee to the temporary classification “was a compromise between (1) the objective of the authors to impose limits of purpose and duration on the authority to hire temporary community college teachers, and (2) the proposal of the local government committee to place virtually all newly hired community college teachers on temporary status.” The Peralta court described temporary teachers hired to teach less than 60 percent of full time: “ ‘They receive a written letter of notification from the district regarding their employment for the coming academic year. The letter states the instructor’s potential assignment and specifies that his position is a temporary one. They are hired from quarter to quarter or from semester to semester, as the case may be. They are uniformly dismissed at the end of each year.’ ” (Id., at p. 376; italics added.)

In 1974, former section 13335 (see current § 87477) was amended to provide: “. . . At the time of initial employment during each academic *921year, each new certificated employee of the school district shall receive a written statement indicating his employment status and the salary that he is to be paid. If a school district hires a certificated person as a temporary employee, the written statement shall clearly indicate the temporary nature of the employment and the length of time for which the person is being employed. If a written statement does not indicate the temporary nature of the employment, the . . . employee shall be deemed to be a probationary employee . . . .” (Stats. 1974, ch. 1239, p. 2684, italics added.)

Because temporary employees, including those hired year after year on a part-time basis, hold positions of a temporary nature and are technically dismissed each year, it would make no sense under the statutory scheme to speak of the layoff of a temporary employee resulting from a reduction in services. Their employment is extinguished each year. If they are to teach successive years, it is only because they have been rehired for a new year (or semester). Because tenured and contract employees have priority over temporary employees, a “reduction in services” and a consequent layoff of tenured and/or contract employees under section 87743 should occur only after a district has decided not to reemploy its temporary teachers.11 For purposes of the reemployment statutes, if the District offers a class previously taught by a temporary employee following a layoff, it has reestablished a service. If it employs someone to teach that class, it has increased the number of employees following the layoff. Any other conclusion would circumvent the priority given to tenured and contract teachers under the statutes.

This position is supported by Poppers v. Tamalpais Union High School Dist. (1986) 184 Cal.App.3d 399 [229 Cal.Rptr. 77], a case involving the construction of analogous layoff and rehire statutes relating to certificated employees teaching grades kindergarten through 12th grade. (§§ 44949, 44955, 44956.) There the petitioner, a tenured teacher, was laid off in 1981 as a result of a reduction in services even though his seniority number was higher than that of a retained tenured employee because the petitioner was not certificated and competent to perform the retained employee’s duties as district grants coordinator/project writer. In 1983, the District decided to eliminate the grants coordinator/project writer position and to transfer the previously retained teacher to a vacant multisubject assignment position which petitioner was credentialed and competent to render. Petitioner challenged the assignment claiming the rehire statute gave him priority to the position because of his seniority;12 his argument was that the language in *922section 44956, i.e., “provided, that no probationary or other employee with less seniority shall be employed to render a service which said employee is certificated and competent to render,” required that he be offered the vacant multisubject position even though the number of employees had not been increased nor the discontinued service reestablished. The First District, concluding that the provision was intended to encompass the transfer of existing employees and that the petitioner was entitled to the position, asserted that the Legislature’s use of the term “employ” rather than “hire” supported that conclusion. The court further asserted: “The statutory purpose of preserving the seniority rights of terminated employees would be patently circumvented if [petitioner] were deemed disentitled to multisubject assignment simply because he was laid off before the position became available.” (Id., at p. 405.)

The Poppers case holds that if a position becomes available which a laid-off employee is competent and certificated to teach, a laid-off senior tenured employee has priority over a retained junior tenured employee. A tenured employee must have at least the same, if not more, rights in relation to a temporary employee. We conclude that pursuant to the rehire statutes, appellants should have been offered classes scheduled in the evenings beginning in the 1982-1983 school year.

The District attempts to get around this unfavorable result by arguing that it offers two distinct types of services, i.e., day classes taught by tenured and contract employees and night classes taught by temporary employees. Its contention appears to be that the day school and evening school are separate entities with separate seniority lists and that there can be no crossover between the two.

We note first that the District has made no claim that it comes under former section 72012 which provided for the establishment of separate day and evening community colleges but was repealed in 1981. (Stats. 1976, ch. 1010, § 2; Stats. 1981, ch. 470, § 45.) Moreover, even assuming the District contended it formed separate colleges under that section prior to its repeal, there is nothing in the record in this case to support a claim of two separate schools; in fact, all the evidence points to the contrary. The schedule of classes included in the record mentions nothing of a separate evening col*923lege. The schedule does not reveal a separate administrative board for an evening college. The most it says about evening classes is “Evening classes offer an opportunity for community involvement as well as crossover registration for day students.” Moreover, the master contract itself reveals there is no dichotomy between day and evening classes. It provides that, although efforts will be made to assign a major portion of the instructional load of regular and contract employees during the hours of 8 a.m. to 5 p.m. Monday through Friday, such instructors may be assigned evening and weekend classes if the “needs of the District dictate.” Thus, the District’s attempts to insulate the evening classes from the reaches of the regular and contract employees on the ground of a separate system or separate “services” is entirely unsupported.

II

The District makes an alternative claim that the collective bargaining agreement precludes appellants from asserting any rights to the evening positions.13 Even assuming arguendo the District correctly interprets the *924collective bargaining agreement, the appellants could not have waived any of their statutory rights by entering into the contract. Section 87485 provides: “[With one exception]14 any contract or agreement, express or implied, made by any employee to waive the benefits of this chapter [ch. 3 ‘Employment’ includes layoff and rehire provisions] or any part thereof is null and void.” (See Hart Federation of Teachers v. William S. Hart Union High School Dist. (1977) 73 Cal.App.3d 211, 214 [141 Cal.Rptr. 817]; Wins-low v. San Diego Community College Dist. (1979) 97 Cal.App.3d 30, 35 [158 Cal.Rptr. 509]; cf. California Teachers’ Assn. v. Parlier Unified School Dist. (1984) 157 Cal.App.3d 174, 183 [204 Cal.Rptr. 20]; Raven v. Oakland Unified School Dist. (1988) 206 Cal.App.3d 742, 750-751 [254 Cal.Rptr. 37] [nonwaiver provision of § 44924 (parallels § 87485 within scheme applicable to K-12) applies to collective bargaining agreements.]15 We recognize that the statutory scheme governing certificated employees teaching grades K-12 provides that the layoff and rehire statutes relating to those employees “shall not be applicable to probationary certificated employees who are covered by a collective agreement which contains provisions for the layoff and reassignment of such employees” if the school district has an average daily attendance of 400,000 or more. (§ 44959.5) However, we have found no comparable provision (nor has the District directed our attention to one) in the Education Code sections relating to the layoff and rehire of community college certificated employees.16 Moreover, the District’s position is that the Education Code does not give laid-off tenured employees the right to teach the evening classes; its argument essentially is that the collective bargaining agreement is consistent with the statutory scheme.

Ill

Having established the appellants’ right to be offered the evening classes beginning in the 1982-1983 school year, we turn to the exhaustion of admin*925istrative remedies question. The District contends that appellants are precluded from asserting any rights to the positions because they failed to assert their rights to “bump” the temporary teachers at the layoff hearing. The District contends appellants should have informed it at the layoff hearing that they wished to teach the evening classes previously taught by the temporary employees. The District’s claim is that the regular and contract employees’ “bumping” rights (i.e., the right of an employee with more seniority to take the position of another with less seniority) should have been exercised against the temporary employees at the layoff hearing. Their failure to do so, argues the District, is a failure to exhaust administrative remedies. We disagree.

As recognized by both sides at the hearing, temporary employees have no statutory right to a layoff hearing. They may be dismissed at will by the District. Regular and contract employees have due process rights to cause and a hearing before they can be relieved. When a community college decides to lay off its regular and contract employees because it is reducing services, presumably it has decided to first cut the temporary employees. That is what the layoff statute presupposes. The layoff statute specifically provides that no regular employee may be laid off while “any probationary employee, or any other employee with less seniority, is retained to render a service” which the regular employee is competent to render. (§ 87743.)

Before the layoff hearing, appellants received individual notices informing them of the particular kinds of services which were to be reduced or discontinued and of their probable layoff. The notices informed them of their right to a hearing and further notified them that “there is no probationary or permanent certificated employee with less seniority retained who is rendering service which you are certificated and competent to render.” The accusation sent to the teachers to be laid off stated that “[t]he district will not retain any probationary employee, or any other certificated employee with less seniority than Respondent, during the 1982-1983 school year to render a service which Respondent is certificated and competent to perform.” (Italics added.)

The notices also informed appellants that the equivalent of 18.78 full-time positions (a figure reduced at the hearing by 1.45) were to be reduced. The number of tenured and contract employees laid off at the hearing equaled this figure. The District said nothing of other positions being reduced or of other positions being retained.

The record reveals that, although some temporary employees received some layoff notices, at the hearing the District and appellants recognized that those employees have no hearing rights and therefore were not includ*926ed in the hearing. At the hearing the District stated it was withdrawing the accusations relating to the temporary employees because they have no right to a hearing.

The seniority list presented by the District at the hearing contained the names of regular and contract employees only. All of the questioning of the superintendent at the hearing related to that list; explanations were made as to why some regular or contract employees were “skipped over” in the layoff because of their specific certifications or competency which more senior employees did not possess.

The District claims that, the above notwithstanding, appellants had notice that the District was going to “retain” some of the temporary employees because only some of the temporary employees received “layoff” notices. Because of this notice, the District’s argument continues, appellants should have exercised their “bumping” rights against those employees.

Under the layoff statutes, “when a service is eliminated the holder of the position is not necessarily terminated, but is entitled to another assignment to which his seniority and qualifications entitle him.” (Otto v. Davie (1973) 34 Cal.App.3d 570, 575 [110 Cal.Rptr. 114].) The layoff statutes “ ‘con-taint ] a mandatory directive to the board to determine whether any employee whose employment is to be terminated for a reduction in attendance or for a reduction in a particular type of service possessed the seniority and qualifications which would entitle him to be assigned to another position.’ ” (Thompson v. Modesto City High School Dist. (1977) 19 Cal. 3d 620, 628 [139 Cal.Rptr. 603, 566 P.2d 237].) “Bumping” rights are exercised by an employee (with notice of termination because of a reduction in services) against a more junior employee who is being retained if the senior employee is credentialed and competent to perform the services being rendered by a more junior employee. (Ozsogomonyan, Teacher Layoffs in California: An Update (1979) 30 Hastings L.J. 1727, 1747-1749.) “Senior employees are given ‘bumping’ rights in that they will not be terminated if there are junior employees retained who are rendering services which the senior employee is certificated and competent to render.” (Alexander v. Board of Trustees (1983) 139 Cal.App.3d 567, 571 [188 Cal.Rptr. 705]; italics added.)

The hearing procedure presupposes some sort of plan on the part of the District as to which employees are to be retained. Only when such a plan is presented does the concept of bumping rights have any meaning. (See Davis v. Gray (1938) 29 Cal.App.2d 403, 408 [84 P.2d 534]: “when it becomes necessary to reduce the number of teachers [and] . . . probationary teachers .. . are engaged in work which the permanent teacher is competent to perform. ... it becomes the absolute duty of the board to first determine *927whether the permanent teacher is competent to perform the duties of any such probationary teacher before he may be discharged. . . . [T]he burden is on the board to show that [the permanent teacher] is not competent to perform the service of a probationary teacher, before she may be discharged”; see also Krausen v. Solano County Junior College Dist. (1974) 42 Cal.App.3d 394, 402 [116 Cal.Rptr. 833]: “[Section 87743’s predecessor] contains a mandatory directive to the board to determine whether any employee whose employment is to be terminated for a reduction . . . in a particular type of service possessed the seniority and qualifications which would entitle him to be assigned to another position.”)

The only “plan” presented by the District in this case was a proposal to reduce certain services by specified amounts. The seniority list presented at the hearing contained only the names of regular and contract employees. The presentation of such a list implies that only those employees listed on it can be bumped. No plan was presented revealing what temporary employees were going to be rehired by the District. Moreover, it would make no sense to attempt to assert “bumping” rights against employees who are routinely dismissed at the end of each term. The positions of those employees were not at issue.

Appellants’ failure to assert a right to the positions later filled by temporary employees where such positions were not at issue at the hearing is not a failure to exhaust an administrative remedy. There was no administrative remedy to exhaust. “The rule that a party must exhaust his administrative remedies prior to seeking relief in the courts ‘has no application in a situation where an administrative remedy is unavailable or inadequate.’ ” (Diaz v. Quitoriano (1969) 268 Cal.App.2d 807, 812 [74 Cal.Rptr. 358]; see also Southern Pacific Transportation Co. v. State Bd. of Equalization (1987) 191 Cal.App.3d 938, 945, fn. 3 [237 Cal.Rptr. 191] and cases cited therein.) The layoff proceedings provide no method for a regular or contract employee who has been notified of his or her imminent layoff to assert rights as against employees who are not on the seniority list and who have not yet been hired for the following year.

Nor does the failure to challenge the layoff within 30 days by writ of administrative mandamus (Code Civ. Proc., § 1094.5) preclude relief here. Appellants could not have raised “bumping” rights against the temporary instructors; likewise, they could not have subsequently challenged the validity of the layoff proceedings on the ground that the District later hired the temporary instructors for the succeeding school year.

IV

The District also repeats its laches claim, arguing that even if appellants had no duty to assert any rights against the temporary employees at *928the hearing, when they received notice of the spring 1982 schedule and the District’s intention to hire temporary instructors that semester they should have asserted their rights at that time. No action was brought by the appellants until Spring 1983. This delay, argues the District, was to the District’s prejudice because the District paid salaries to the temporary employees for that year. The District argues additionally that it was prejudiced by the delay because, under the collective bargaining agreement, the temporary employees can only be fired for cause. The District contends that if it allows the appellants to fill in for the classes taught by the temporary instructors, it will be subject to multiple lawsuits from the temporary employees. These two contentions are the bases of its prejudice claim.

We note initially that section 87744 provides that laid-off tenured employees offered reemployment may waive their right to reappointment for up to one year. An employee’s failure to assert a right to reemployment where the District has failed to comply with the statute should put the District in no worse position than if it had offered the positions that first year and the appellants had waived their rights to reappointment.

Next we note that the collective bargaining agreement does not contain a definition of the type of “cause” that would justify “termination” of a temporary employee.17 (Cause for termination of a regular or contract employee is provided in the Education Code.) To the extent a “failure to rehire” is considered a “termination,” a failure to rehire because a tenured employee has a superior right to teach that class would be a sufficient cause.18 The “Layoffs and Termination” provision of the master contract relating to temporary employees expressly recognizes the right of full-time instructors to “replace” the temporary, part-time instructors. (See fn. 13, supra.) Moreover, even assuming arguendo the correctness of the District’s implicit assertion that a tenured instructor’s preferential right to the position is insufficient cause to justify failing to rehire a temporary employee, appellants’ delay in bringing this action would have no bearing on any alleged prejudice to the District. If the appellants did not receive notice of the hiring of the temporary employees until the spring schedule was mailed, any immediate protest by appellants would put the District in the same position it was in with regard to the hired employees when this action was filed.

We next consider the claim that the District would be prejudiced by appellants’ delay in the assertion of their rights because it already paid *929salaries to the temporary employees for the 1982-1983 school year (before this action was filed) and any acknowledgment of appellants’ rights to those positions would result in double payment for that year. The District appears to acknowledge that if appellants waive any rights to salaries for that year, any vestige of prejudice relating to the double payment would be eliminated. (See Conti v. Board of Civil Service Commissioners (1969) 1 Cal.3d 351 [82 Cal.Rptr. 337, 461 P.2d 617].) However, the District urges that such prejudice has not been eliminated here because appellants have not waived any right to backpay. “In the absence of a waiver,” the District argues, “the trial court properly determined that the potential back pay liability constitutes substantial prejudice to the District.”

What the District fails to recognize, however, is that the stipulated issue before the trial court was the District’s obligation to offer appellants the evening classes starting with the 1982/1983 school year. The question of damages was deferred for a later hearing. With the issue framed for the court as a question of the parties’ legal rights, it is no wonder appellants expressed no view on the double payment problem. Given the posture of the case, their failure to waive any rights to pay for the 1982-1983 school year should not prevent them from exercising their rights to the positions from the time of the filing of the action. The question of their rights to damages with respect to any school year was deferred.

The trial court erred in concluding that the prejudice requirement for a laches claim was met. The court also erred in relying on an estoppel defense when such was neither pleaded nor argued by the District. (See 5 Witkin, Cal. Procedure (3d ed. 1985) Pleading, § 1044, pp. 460-461.)

Disposition

Appellants had a right to be offered the evening classes following the layoff. The judgment is reversed. We remand the case to the trial court for consideration of the bifurcated issue of damages, commencing with the 1983-1984 school year. Appellants shall be awarded their costs on appeal.

Carr, J., concurred.