Economists Julian Betts and Emily Tang reviewed 40 high-quality studies of charter school achievement and analyzed the results. They found modest gains despite variation among charter schools. For example, the largest average effect, for math achievement in middle schools, suggests that on average a charter school attendee would gain about two percentile points per year relative to his or her counterparts in traditional public schools.
The authors found no substantial difference on average in math or reading achievement between traditional and charter high schools or in reading achievement at the middle school level.
The researchers found that charter school effects vary dramatically across regions and grades. For instance, while overall the effect of charter schools at the middle school level is small and insignificantly different from zero, one recent study of Boston schools found very large and positive effects. The analysis also suggests that urban charters perform better than suburban or rural charters, especially at the middle and high school levels.
In their report, The Effect of Charter Schools on Student Achievement: A Meta-Analysis of the Literature, Betts and Tang provide a fresh overview of the currently available research, focusing on only those studies using high-quality approaches that are more likely to yield valid results. They state that, “Examining all of these results as separate parts of a whole, charter schools look to be serving students well, at least in elementary and middle schools, and probably better in math than in reading. There appears to generally be more variation in the results for math than in reading.”
Robin Lake, the center’s associate director, who commissioned the report, said that, “opponents and proponents are tempted to point to one or two studies that confirm their point of view. The advantage of the meta-analysis is that it looks at the entire body of rigorous research and discerns what it is saying overall. There are indeed individual studies that show charters have quality issues that need to be addressed, but on the whole, charter schools generally seem to perform well.”
As in their 2008 literature review (also published by the center), Betts and Tang note the wide disparity in the quality, and therefore the validity, of studies of charter schools. This can be a problem for journalists and others who want to know whether a given study is scientifically valid, or whether findings from one study can be generalized to charter schools overall. To address this, the center has published Making Sense of Charter School Studies: A Guide for Reporters; the guide is available at www.crpe.org, as is the new report and a short summary brief.