Harvard’s Caroline Hoxby has produced a new analysis of charter school achievement (pdf). Rather than the NAEP sample data which has garnered so much attention, Hoxby was able to analyze almost the entire universe of 4th-graders attending charter schools and compare their achievement in reading and math on state assessments to students at the schools they most likely would have otherwise attended. Where 4th-grade data was not available she used 3rd-or 5th-grade data. It’s a much more sophisticated study than the recent AFT report (pdf).
Her findings? In every case – except one – where there was a statistically significant difference (at .90 or .95) between public charter schools and the schools charter students would have otherwise attended the difference was positive in favor of public schools. The exception? You guessed it, North Carolina. Nationwide, average gains were small but positive. That’ll be the headline; however, because the study is based on state tests this finding is less relevant than the state-by-state data.
Unfortunately, Hoxby’s study, too, is limited to elementary schools. More data on charter high schools would be useful as well. And, because some states have fewer than 200 fourth-graders in charter schools they could not be analyzed. Hoxby notes that because the numbers of charter school students are relatively small overall, it’s just too soon to jump to sweeping conclusions about whether the charter idea “works”. Still, although it would be helpful if Hoxby also published the raw numbers her analysis produced, overall the study is transparent, accessible, and pretty useful. Surely you’ll be reading all about it in the NYT any day now.
Cartography Afterthought: Hoxby previously used rivers to draw inferences about parental choice. This study uses longitude and latitude to locate schools. Was she a map maker or explorer in a previous life? Should her nickname be “Topo”?
Update: Welcome Drezner readers. And, Ed Week has more on Topo Hoxby’s study. Duke’s Helen Ladd raises a good point about the snapshot nature of the study but (a) that didn’t stop boosters of the AFT study and (b) for a national study, Hoxby’s efforts are pretty good. Not every state has an assessment and data system that allows for the kind of study that Ladd did in North Carolina.