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For the Common Good: The Spillover Effects of Charter Schools on Public School Students in New York City

Do students in charter schools achieve at higher levels than their otherwise similar peers attending traditional public schools? Is one charter network more effective than another? These questions, often described as “horse-race” questions, are typical of those addressed by the research fueling the charter school debate.

In an article recently accepted by Education Finance and Policy, a peer-reviewed journal, Sarah Cordes, a professor at Temple University, addresses a different question: Do charter schools affect the outcomes of students in traditional public schools? Indirect or “spillover” effects are notoriously difficult to estimate, and Cordes is among the first to take on the challenge in the charter context.

Using data from New York City, she found that charter schools significantly increase achievement for students in traditional public schools in both English Language Arts and math and decrease the probability of grade retention. Effects increase with charter school proximity and are largest in traditional public schools co-located in buildings with charter schools.

The findings suggest that more charter schools in New York City may be beneficial, on average, for both their students and those attending nearby traditional public schools. They also justify efforts to replicate Cordes’s study in other jurisdictions, and to understand why charters exert spillover effects.