D.C. Code § 38-1414

For the purposes of § 38-1412 and § 38-1416, regulations of the Secretary shall include provisions relating to the determination of the number of students enrolled in a school, or in a particular year-class in a school, as the case may be, on the basis of estimates, or on the basis of the number of students who were enrolled in a school, or in a particular year-class, as the case may be, in an earlier year, or on such basis as he deems appropriate for making such determinations.