By Carol Lloyd

Recent national studies found many students in charter schools were not performing as well as those in neighborhood public schools now shows that in a few states, charter schools are improving in some areas, while losing ground in others.

The study, by Stanford University researchers at the Center for Research on Education Outcomes, examined the standardized test results of students enrolled in charter schools in 25 states. The charter school results were compared with those of students with the same demographics and academic profiles in public schools that the charter students would have otherwise attended.

The original study, conducted four years ago, showed that only 17 percent of charter schools managed to raise student math test scores above those of local public schools. The new report said that 29 percent of charter schools performed better in math than local public schools.

And while the 2009 study showed 37 percent of charter schools were actually providing a worse education than local public schools, that figure declined to 31 percent in the new report.

“At both ends of the quality curve, we see that the situation is getting better,” said Margaret Raymond, the center’s director.

Still, the report is likely to provide fodder for critics of charter schools, which are publicly financed but privately operated. More than two million students attend about 6,000 charter schools in the United States.

“Twenty years after the start of the charter school movement, even with all the private energy and public policy cheerleading it has engendered, students in charter schools roughly perform the same as students in the rest of public education — not the leaps and bounds that were promised,” Randi Weingarten, the president of the American Federation of Teachers, said in a statement.

The study concluded that charter schools, which are typically given more freedom to design curriculum and hire nonunion teachers than traditional public schools, range widely in quality from state to state.

While charter schools on average produced better results in states including Louisiana, Massachusetts, Michigan, New Jersey, New York, Rhode Island and Tennessee, as well as Washington, D.C., in some states, including Arizona, Nevada, Ohio, Pennsylvania and Texas, the results were worse — in some cases, significantly worse.