Senator Obama apparently felt free enough from obligations to the American Federation of Teachers, which is meeting in his home city of Chicago, that he skipped their convention and appeared by video. The AFT had endorsed Mr. Obama’s opponent, Senator Clinton, in the Democratic primary. Too bad Mr. Obama doesn’t feel free enough to deviate from the union’s policy agenda.

That he is captive to it was made clear by his prepared remarks. “What I do oppose is using public money for private school vouchers. We need to focus on fixing and improving our public schools; not throwing our hands up and walking away from them,” Mr. Obama said. During the primary campaign, in Wisconsin, Mr. Obama had suggested he would be open to vouchers if empirical research showed that they improved educational outcomes. His new stance — the latest in what seems like a never-ending series of flip-flops — seems to foreclose any support of vouchers, ever, no matter what the research shows.

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The truth is that research has shown that vouchers do improve government-run schools by creating competitive pressure. As Jay Greene wrote recently in City Journal, “In Florida, where wide-ranging incentive reforms have been in place for several years, there have been four rigorous analyses of the effects of competitive pressure on the public school system. All four, from groups as disparate as the Manhattan Institute and the Urban Institute, agree that public schools made exceptional improvements in response to competitive pressure.” So vouchers do improve the government-run schools.

More broadly, the measure of education policy shouldn’t be what effect it has on the government-run schools but what effect it has on educational outcomes for children. The idea that it is “public” money that would be used for vouchers exposes the flaw in Mr. Obama’s thinking; the money only became “public” after it was seized by tax collectors from the parents of the schoolchildren. It’s the parents’ money.

As for “throwing our hands up and walking away” from public schools, that is what Senator Obama did when it came time to choose a school for his two daughters, who go to a private school. All voucher advocates are saying is that parents who don’t have the wealth of the Obamas nonetheless deserve the same option to educate their children that the senator and his wife have.