The constitutional argument against school vouchers is receding—as it should, for it was never terribly convincing. Voucher opponents insist that granting public money to students seeking religious educations violates a core constitutional principle. But at the time of the framing of the Constitution, and throughout the 19th century, public money flowed freely to religious schools. The nation "discovered" the constitutional ban only toward the end of that century, when Catholic schools began seeking support. Only anti-Catholic prejudice can really explain the abrupt shift in national practice.

What's more, it is hard to find a rule based on the Constitution that would allow us to distinguish between a federal grant that helps a poor freshman attend a religious college and one that helps a poor 12th-grader attend a religious high school. But we do the first without murmur of complaint from strict separationists.

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The second prong hinges on whether poor students who exit public schools get better educations. Statisticians run countless regression analyses to find out, but of course, what they are really measuring is the ability of students to take standardized tests. Certainly there are parents for whom high test scores are the principal goal of education, but that is a narrow, even vulgar, vision of what schools are for.

I support vouchers because I support parents. We should both applaud ...