Advocates of separating church and state frequently - and correctly - recite the first phrase of the First Amendment: "Congress shall make no law respecting an establishment of religion . . .," to support arguments against state-sponsored activities and expressions of faith. But the second half of that Establishment clause, "or prohibiting the free exercise thereof;" is less frequently pondered. It is that "free exercise" language, however, around which entwines the case of Joshua Davey, now before the Supreme Court. The ruling could greatly expand the choices of those being educated with government dollars and, in the process, help erase...