The United States Supreme Court has held that parochial schools' good-faith, reasonable reliance upon an untested state aid program that was subsequently declared unconstitutional as involving "excessive entanglement" of church and state, justified a district court order that allowed reimbursement for services rendered prior to the program's invalidation.
Lemon v. Kurtzman, 411 U.S. 192 (1973).
Stephen F. Ban,
Constitutional Law - First Amendment - Establishment Clause - Retroactive Effect,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol12/iss3/18