A federal study showing that fourth graders in charter schools score worse in reading and math than their public school counterparts should cause some soul-searching in Congress. Too many lawmakers seem to believe that the only thing wrong with American education is the public school system, and that converting lagging schools to charter schools would cause them to magically improve.

The study, based on data from 2003 on students' performance on the National Assessment of Educational Progress, found charter school students significantly behind their non-charter-school counterparts. But it also showed that not all charter schools are created equal.

On average, charter schools that were affiliated with public school districts performed just as well as traditional public schools. That may be a disappointment to advocates who expected them to show clear superiority. But the real stunner was the performance of free-standing charter schools, which have no affiliation with public school systems and are often school districts unto themselves. It was this grouping that showed the worst performance.

Free-standing charter schools often bite off more than they can chew. The presumption is that without the bureaucratic restraints of the public school system and the teacher unions, charter schools can provide better education at lower cost. But the problem with failing public schools is that they often lack both resources and skilled, experienced teachers. While there are obvious exceptions, some charter schools embark on a path that simply recreates the failures of the schools they were developed to replace.

Charter school advocates denounced the new federal study even before it was released and took issue with its methodology, which is not perfect. But this study does not stand alone. The evidence so far shows that charter schools are not inherently superior to the traditional public schools they often seek to supplant — and that they are sometimes worse.

One advantage of the No Child Left Behind Act of 2002 was the wave of education studies it started. They offer hope that Congress will look at the record when it considers reauthorizing the law next year. If it does, lawmakers will back away from the part of the act that offers charter schools as a cure-all. They should instead home in on the all-important but largely neglected issue of teacher training and preparation — which trumps everything when it comes to improving student achievement.

These studies argue for a more nuanced federal policy that does not just advocate wholesale charter conversion but instead defines and supports successful models only. Beyond that, Congress needs to grasp the obvious, which is that the quality of the teacher corps is more crucial to school reform than anything else. The original law required states to provide highly qualified teachers in core subject areas by this year. But the Education Department simply failed to enforce the rule, partly because of back-channel interference by lawmakers who talked like ardent reformers while covering up for state officials clinging to the bad old status quo.

Four years later, the national teacher corps is still in a shambles. Until Congress changes that, everything else will amount to little more than tinkering at the margins.

Commentary: