In our fruitless, deadlocked debate over whether charter schools “work," charter opponents frequently cite the so-called CREDO study (discussed here), a 2009 analysis of charter school performance in 16 states. The results indicated that overall charter effects on student achievement were negative and statistically significant in both math and reading, but both effects sizes were tiny. Given the scope of the study, it’s perhaps more appropriate to say that it found wide variation in charter performance within and between states – some charters did better, others did worse and most were no different. On the whole, the size of the aggregate effects, both positive and negative, tended to be rather small.
Recently, charter opponents’ tendency to cite this paper has been called “cherrypicking." Steve Brill sometimes levels this accusation, as do others. It is supposed to imply that CREDO is an exception – that most of the evidence out there finds positive effects of charter schools relative to comparable regular public schools.
CREDO, while generally well-done given its unprecedented scope, is a bit overused in our public debate – one analysis, no matter how large or good, cannot prove or disprove anything. But anyone who makes the “cherrypicking” claim is clearly unfamiliar with the research. CREDO is only one among a number of well-done, multi- and single-state studies that have reached similar conclusions about overall test-based impacts.
This is important because the endless back-and-forth about whether charter schools “work” – whether there is something about "charterness" that usually leads to fantastic results – has become a massive distraction in our education debates. The evidence makes it abundantly clear that that is not the case, and the goal at this point should be to look at the schools of both types that do well, figure out why, and use that information to improve all schools.