Some very bad ideas about the relation of church and state have been hanging around schoolyards for many years. In June, the Wisconsin State Supreme Court had the courage to expel those ideas. In Jackson v. Benson, the court weighed complaints against a key experiment in school vouchers and declared that they flunked.

The original Milwaukee Parental Choice Program (MPCP) had allowed only 1.5 percent of the students in the Milwaukee Public Schools to attend a private "nonsectarian" school of their choice at taxpayer expense, as long as their family income did not exceed 1.75 times the federal poverty level. But the law was amended in 1995 to raise the ceiling to 15 percent of mps students. It also shifts the flow of funds from direct-to-schools payments to vouchers that require parental endorsement, limits how much tuition the state will pay, and—here's the rub—no longer restricts the program to "nonsectarian" schools.

Entrenched school bureaucracies in urban centers will be opposed to any expansion of school choice that allows students and tax money to flow elsewhere. But striking the word nonsectarian from the law has moved them from just wagging their jaws to gnashing their teeth.

Opponents of the amended MPCP confronted the Court with two tired and hoary arguments: that any money that ultimately flows to religious schools constitutes an establishment of religion; that government neutrality toward religion means dealing with secular schools only.

The Wisconsin court used criteria developed by the U.S. Supreme Court in 1971 to test these challenges. Those criteria, known as the Lemon test, include three questions: Does the law have a secular purpose? Will its principal effect neither enhance nor inhibit religion? ...