In Board of Educ. v. Allen, 392 U.S. 236, 88 S.Ct. 1923, 20 L.Ed.2d 1060 (1968), the Court upheld a law requiring public school authorities to lend textbooks, free of charge, to all students of public and private schools. Such a program did not serve to advance religion because, inter alia, "the law merely makes available to all children the benefits of a general program to lend school books free of charge." Allen, 392 U.S. at 243, 88 S.Ct. at 1926. The fact that "free books make it more likely that some children choose to attend a sectarian school ... does not alone demonstrate an unconstitutional degree of support for a religious institution." Id. at 244, 88 S.Ct. at 1926-27. Allen thus rests on the robust principle that "the Establishment Clause does not prevent a State from extending the benefits of state laws to all citizens without regard for their religious affiliation." Id. at 242, 88 S.Ct. at 1926.