Champions of charter schools were dealt a sobering reminder of their core mission recently: to innovate effective and new education models that can be successfully channeled into the nation’s broader public school system. A new report from Stanford University’s Center for Research on Education Outcomes questions whether this, after 20 years, is happening.

According to the CREDO report, about 17 percent of charter schools had academic gains significantly higher than traditional public schools, 37 percent performed worse, and about 46 percent showed no significant difference.

The report examined charter schools in 15 states and the District of Columbia, with more than 70 percent of nation’s charter school students. Despite considerable demand for charter schools by parents and support from the business community, charter schools vary widely in quality, the report says. And it warns that states need to take steps to more quickly evaluate and close low-performing charters.

However, the report also says that low-income students and English language learners showed more significant gains in charter schools than they did in traditional public schools . And students overall performed better the longer they attended charter schools.

Critics and supporters of charter schools issued their position statements for and against the latest CREDO report. Overall, the report doesn't reveal a lot that we don’t already know. But it does continue to raise questions about the real purpose of charters, and where the charter school movement is headed.