The nation’s public charter schools are growing more effective but most don’t produce better academic results when compared with traditional public schools, according to a report released Tuesday.

Researchers at Stanford University’s Center for Research on Education Outcomes looked at test data from charter schools in 26 states and the District and found that 25 percent of charters outperformed traditional public schools in reading while 29 percent of charters delivered stronger results in math. That marked an improvement over a similar 2009 study by the same research team.

But 56 percent of the charters produced no significant difference in reading and 19 percent had worse results than traditional public schools. In math, 40 percent produced no significant difference and 31 percent were significantly worse than regular public schools.

States that shuttered at least 10 percent of their charter schools — the worst performers — had the best overall results, the study found.

In the District, where 43 percent of public school children attend charters, there were significant gains. Children attending D.C. charter schools did better in both reading and math when compared with those attending traditional public schools, the study found.

“We’re popping the champagne corks here,” said Scott Pearson, executive director of the D.C. Public Charter School Board. “We think it’s a very strong affirmation of the power of charter schools when they’re done right.”

Louisiana, Tennessee and Rhode Island also showed strong results, while Nevada, Ohio, Oregon and Pennsylvania were among the weakest.

Several factors helped fuel the success of charter schools in the District, Pearson said. “D.C. is a very special environment,” he said. “We have a model law, an authorizer with an unusual independence and an incredible ecosystem with support organizations that help our schools. Our schools have formed a real community amongst themselves.”

And yet, Pearson said, “the national picture is still dismal.”

The District led the pack in shutting down weak charters, with the city closing about one-third of its charter schools.

And that effort needs to be mirrored throughout the country, the researchers said. “Low-performing schools are not being shut quickly and low-performing schools are being permitted to replicate,” the study said.

Public charter schools are funded with tax dollars but operate independently of the traditional public school system. Most are not unionized and some are run by for-profit companies.

The question of how charter schools compare with traditional public schools is growing increasingly important as they proliferate across the country, thanks in part to federal policies Congress and the Obama administration have promoted.

About 2.3 million students were enrolled in roughly 6,000 public charter schools in the academic year that just ended. That is still less than 5 percent of the country’s 50 million public school children.

Nina Rees, president of the National Alliance for Public Charter Schools, found the study encouraging. “The numbers are trending in the right direction,” she said.

But critics, many of whom think charters siphon away needed tax dollars from traditional public schools, said the study weakens the case for continued investment.

“This seems to go along with a host of other reports that basically says there’s no difference between charter schools and traditional public schools,” said Andy Maul of the University of Colorado’s National Education Policy Center.

Greater numbers of minority and poor students with academic deficits are attending public charter schools now than in 2009, said Margaret Raymond, director of the Center for Research on Education Outcomes. That would seem to contradict a widely repeated criticism that charters attract motivated families while public schools are left to absorb the most challenged students, she said.

The study found that poor children, particularly African Americans and Hispanics, made the greatest gains in charters while children who are not poor — no matter their race — gained nothing or even performed worse than their counterparts in traditional public schools. Hispanic students who are English language learners also made gains in reading and math in charter schools.