For years, free-market school reformers have complained that teachers unions and educational bureaucracies were blocking the path of necessary change. They have persuaded policy makers in several large cities to challenge the established culture through means such as charter schools and merit pay. But when their ideas are tried and don't succeed, they can be slow to admit that their own programs should be open to challenge as well.

For the past five years, Philadelphia has engaged in the nation's biggest experiment in private management of public schools. When Pennsylvania took over the schools in 2002, state officials wanted to hand the entire running of the district over to Edison Schools Inc. That didn't fly politically, but Edison and several other operators were brought in to manage 45 of the 250 schools in the district.

The results are starting to show, and they don't look so hot for the private managers. A study of four years' worth of reading and math scores released by the RAND Corp. in February found that student achievement had improved at the privately managed schools--but not any more than in the district as a whole. In fact, the only schools to post faster gains were 21 "restructured" schools to which the district itself had devoted more resources.

The findings have since been more or less replicated by local studies. But the reformers have attacked RAND's methodology and conclusions on blogs and in venues as prominent as the Wall Street Journal op-ed page. "For me, at least, the study completely misses the mark," says Charles Zogby, a consultant who served as Pennsylvania's education secretary during the district takeover. "Any reform in education is held to this standard of perfection, when the public school system itself is indisputably inadequate."

One of the main complaints of the free-market critics is that Philadelphia doesn't offer a true test of market competition. The private managers have to abide by union contracts and other district policies. Still, many of these same critics had long hailed Philadelphia as the shape of things to come. "They have hyped and overpromised in Philadelphia," says Frederick Hess, author of the book "Common Sense School Reform," "and they are dealing with the consequences."

Eventually, someone will come up with a better way of educating children in this country than the models that have been tried, but there are bound to be plenty of failures along the way. The reformers should admit that some of their ideas will not pan out quite as well as they had anticipated, rather than denying proof of failure or even mediocre results whenever they appear.