The Evidence on Charter Schools
In our fruitless, deadlocked debate over whether charter schools "work," charter opponents frequently cite what is often called the CREDO study (discussed here), a 2009 analysis of charter school performance in 15 states and the District of Columbia. The results indicated that overall charter effects on student achievement were negative and statistically significant in both math and reading, but both effect 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