Stuart Buck, author of the terrific Acting White, offers a brief discussion of how to think about assessments of charter school performance:
We’ve heard about several studies indicating that charter schools don’t have a higher average effect than regular public schools. Take, for example, this Mathematica study of charter schools in 15 different states. It found no overall impact on the students. But this masks an important variation in who benefited and who didn’t:
We found that study charter schools serving more low income or low achieving students had statistically significant positive effects on math test scores, while charter schools serving more advantaged students—those with higher income and prior achievement—had significant negative effects on math test scores.
In other words, charter schools were doing very different things for different students — raising up low income and poor-scoring students while actually harming richer and higher-scoring students’ test scores.
Average them all together, and you find no effect. But if you want to expand charter schools in impoverished urban areas, the “no overall average benefit” finding would be completely beside the point.
As Buck goes on to observe, a new study of Milwaukee charter schools, by Hiren Nisar, made a similar finding about the the contrast between average charter school performance and the extremely impressive impressive results charter schools have had with low achieving students. I recommend the post.
This reminds me of the commonplace observation that while charters might work for some students — say, students with engaged parents — the poorest, most difficult-to-educate kids don’t benefit from charters. One gets the impression that the opposite is true. Better-off students don’t need charters, while poor students seem to get a lot out of them.
Moreover, one could argue that charter school performance with more affluent, higher-achieving students masks other aspects of what we might call “customer satisfaction,” i.e., the students may not test as well, but we’re seeing revealed preference at work. (Imagine middle-class parents choosing to send a child to a progressive arts-focused charter, where reading and math scores are lackluster relative to a conventional school but results in other domains, like the life satisfaction of idiosyncratic students, are impressive.) This can’t really be said of students attending schools in districts where choice only exists if one has the resources to move or to pay for a parochial or independent school out of pocket.
