As charter schools continue to proliferate across the country, a new study finds that they are offering benefits for students with disabilities.

In a report out this week, the Center for Research on Education Outcomes at Stanford University compared the performance of students at charters with that of students attending traditional public schools in 25 states, the District of Columbia and in New York City. The analysis is an update to a similar report issued in 2009.

Overall, the study finds that charters are improving, particularly when it comes to often-underserved groups like poor and minority students and those with disabilities.

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To assess students in special education, researchers compared those attending charters to students at traditional public schools by matching children who started out testing at the same level in order to mitigate the influence of their disability. Then, they looked at standardized test results from the same students years later to determine which schools they fared better in.

While gains in reading were similar for the two groups, the report found that special education students at charters saw greater advances in math, equivalent to 14 extra days of learning.

“The results reveal that the charter school sector is getting better on average and that charter schools are benefiting low-income, disadvantaged and special education students,” said Margaret Raymond, director of the Stanford center that produced the analysis.

The study authors indicated that the gains in recent years could be attributed, at least in part, to the closure of poor-performing charter schools.

In a statement, the president of the American Federation of Teachers, Randi Weingarten, said that the findings show students at charters “roughly perform the same” as those at other schools and indicated that charters are failing to provide “the leaps and bounds that were promised.”

“While any gain in achievement is welcomed, we should use the CREDO findings as an opportunity to pause and ask ourselves why we keep pitting charter schools against neighborhood public schools — a strategy that has created little more than a disruptive churn,” Weingarten said.

Enrollment at charters has ballooned by 80 percent since the 2009 report, with more than 2.3 million American kids now attending over 6,000 schools in 41 states, researchers said.

However, students with disabilities are still less likely to attend charter schools over traditional public schools, according to the analysis. Special education students account for 13 percent of public school students across the country, but represented just 8 percent of the students at charters examined for the report.