In Witters v. Washington Dept. of Servs. for Blind, 474 U.S. 481 (1986), the Court rejected an Establishment Clause challenge to a vocational scholarship program that provided tuition aid to a student studying at a religious institution to become a pastor.
The Court observed, taking the program as a whole, that "any aid ... that ultimately flows to religious institutions does so only as a result of the genuinely independent and private choices of aid recipients." 474 U.S. at 487.
The Court further remarked that, as in Mueller v. Allen, "[the] program is made available generally without regard to the sectarian-nonsectarian, or public-nonpublic nature of the institution benefited." 474 U.S. at 487. In light of these factors, the Court held that the program was not inconsistent with the Establishment Clause. Id. at 488-489.