These consolidated cases are appeals pursuant to G. L. c. 58A, § 13, from the decisions of the Appellate *482Tax Board (board) granting abatements to the appellees, taxpayers, from real estate taxes levied in the years 1977 through 1979. The appellant board of assessors of the city of Boston (city) challenges the board’s ruling that the lowest substantial class of real property in the city of Boston was the so called R-l single family residential, or single dwelling unit residential class. The city contends that the board’s ruling is erroneous (1) because the board failed to state its reasons or make findings of fact in support of its determination that the R-l class, as opposed to the class of all residential property, is a separate and distinct class for the purpose of real property classification; (2) because the selection of the R-l class has no rational basis in law or fact; and (3) because the board’s determination is inconsistent with the policy underlying the recently approved classification Amendment to the Massachusetts Constitution2 and the legislative responses to that amendment.3

The determination whether single family residences constitute a “class” for tax abatement purposes is a mixed question of fact and law. As the board is a State agency charged with administering the tax abatement process, its determination is due some deference. See Henry Perkins Co. v. Assessors of Bridgewater, 377 Mass. 117, 121-122 (1979). We have long recognized the board’s expertise in tax matters. See Assessors of Quincy v. Boston Consol. Gas Co., 309 Mass. 60, 72 (1941). The board has adequately set forth and the record supports the factual predicates for its determination.*4834 Cf. G. L. c. 58A, §§ 10 and 12C. Moreover, this determination is in no respect inconsistent with our past declarations of the appropriate remedy available to a taxpayer whose real estate taxes have been disproportionately assessed. See, e.g., Tregor v. Assessors of Boston, 377 Mass. 602, 611-612, cert, denied, 444 U.S. 841 (1979); Beardsley v. Assessors of Foxborough, 369 Mass. 855 (1976); Shoppers’ World, Inc. v. Assessors of Framingham, 348 Mass. 366, 377 n.10 (1965). “[A] taxpayer has a right to have his assessment reduced so that it is ‘proportional to the assessments of the class of property valued at the lowest percentage of fair cash value.’” New Boston Garden Corp. v. Assessors of Boston, ante 456, 458 n.3 (1981), quoting from cited cases. Cf. Chomerics, Inc. v. Assessors of Woburn, 6 Mass. App. Ct. 394 (1978). Finally, the board’s ruling is not inconsistent with the Massachusetts Constitution or any legislation as in effect during the tax years in question.5

The decisions of the Appellate Tax Board are therefore affirmed. Costs of the appeal are to be awarded to the taxpayer in each case.

So ordered.

Justice Kaplan participated in the deliberation on this case, but retired before the opinion was issued.

(concurring, with whom Hennessey, C.J., joins). If one accepts the view expressed by the court in *484Tregor v. Assessors of Boston, 377 Mass. 602, 611-612 (1979), that the taxpayers are entitled to abatements to the level of the class of property that is valued at the lowest percentage of-fair cash value, the result reached by the court in this case is correct. I did not, and do not, agree with the view expressed by the court in its Tregor opinion. See Tregor v. Assessors of Boston, supra at 613 (Wilkins, J., dissenting, with whom Hennessey, C.J., joins). However, because the point has not been raised anew and the court in the Tregor case established the rule of law to be applied in this case, I join in the opinion in this case.