The California Charter Schools Association (CCSA) today released their first self-study, “Portrait of the Movement“. The report uses a modeling tool developed by the study’s authors to weigh a school’s Academic Performance Index (API) against a predicted API that controls for factors in a student’s background such as poverty. The CCSA concludes that charter schools both out- and under-perform traditional schools in California. Study results indicate that in California, charter schools are four times as likely to rank in the top 5% of schools and twice as likely to rank in the bottom 5%. The study does not disaggregate data from “turnaround” or “conversion” charter schools (that enroll all students from a traditional school) versus “schools of choice” (where families self-select the charter school). The most widely referenced data on charter school performance was an independent national study conducted by Stanford University’s Center for Research on Educational Outcomes (CREDO) in 2009. That study concluded that 17% of charter schools nationwide outperform conventional schools while 37% show lower gains than their traditional public school counterparts.