This paper quantifies the religious factor in education demand by calibrating a political economy model of education finance and school choice in which parents who differ in the advantage they attribute to religious education choose from among public, private-nonsectarian, and religious schools. The calibrated distribution of religious preferences indicates that the revealed advantage of religious education is strongly contingent on its high levels of subsidization. The results of the calibration are applied to compare the effect of publicly funded vouchers that do not exclude religious schools--to which the Supreme Court recently opened a door in Zelman v. Simmons-Harris--with vouchers restricted to nonsectarian schools. It supports the implicit conclusion of the Supreme Court, that participation of religious schools in the Cleveland voucher program was essential for achieving its goal of helping low-income parents in a failing school district. Larger vouchers would have reduced the share of religious schools in the program, though they would still have attracted a majority of students. (Contains 40 references, 44 endnotes, 8 tables, and 4 figures.) (Author/SM)