Chicago’s charters look pretty good in a new study by the Center for Research on Education Outcomes at Stanford University. But the study gives charters nationwide a bit of a black eye.  Already the American Federation of Teachers is using the results as a political battering ram.

The new report provides one of the most sweeping views of charter school performance to date, culling student-level test data from thousands of charters in 16 states, including Chicago’s charter schools. All told, nearly 70 percent of the nation’s charter school students are included in the analysis, which found wide ranging quality among charters and an overall lag in their test score gains.

The study compares test scores for every charter student with a “virtual twin” or demographically similar student who still attends the traditional public school that the charter student left behind. Only students in grades 3 through 8—testing grades required by No Child Left Behind—are included.

Researchers found that 37 percent of charters came up short in the student-to-student comparisons and 46 percent showed no statistically discernable difference. Only 17 percent posted gains that significantly exceeded those made by their twins.

Chicago was among the geographic areas where charters significantly outperformed traditional public schools in math. Reading gains were indistinguishable, statistically.

The researchers also looked at student performance by demographic groups and found higher gains for low-income students and English language learners in charter schools. But African American and Latino students, as a whole, performed better in traditional schools. Results were similar in Chicago, although English language learners did not post significant gains in Chicago’s charters.

The report also found evidence that charters did worse in states with multiple charter authorizing bodies, perhaps a result of what’s known in charter circles as “forum shopping.” That’s where a weak charter management organizer that is turned down by one authorizing body takes its pitch to another, more receptive one. In Illinois, school districts are authorizers, and the Illinois State Board of Education is a backup. A bill awaiting the governor’s signature would set up a task force to investigate the possible impact of a new state authorizer.

In good news for charter proponents, the researchers found that states with caps on charters also reported significantly lower academic results among their charters. Illinois lawmakers recently voted to dramatically increase the state’s charter caps in exchange for new accountability rules for charters.

But the American Federation of Teachers argued that “the inconsistencies in the quality of charter schools should give pause to those who want to lift charter caps, particularly when they are not matched with calls for legislatures to increase accountability.”

They go on to note that some of the better performing states have relatively fewer charters:

“The states with charter schools outperforming regular public schools have fewer charter schools: Arkansas, Illinois (Chicago), Missouri and Louisiana have less than 100 charters each, and Colorado has 140 charters. This pattern strongly suggests that students are not well-served by state or federal policies that encourage unchecked charter proliferation without a rigorous entry process, adequate oversight or speedy closure policies.”

For its part, the National Alliance for Public Charter Schools has raised questions about the study’s methodology, contending it did not adequately match charter students to demographically similar students in traditional schools. Also, larger states were overrepresented in the study, it said.

The Multiple Choice: Charter School Performance in 16 States report is available for download on the CREDO website.

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