CREDO Charter School study

[essentialsaltes]

This is news a year old, but I just spotted that Stanford's Center for Research on Educational Outcomes did a study of charter schools (executive summary here) and found that on average, they did worse than public schools:

Charters whose math growth exceeded their TPS equivalent growth by a significant
amount account for 17 percent of the total.
The remaining group, 37 percent of charter schools, posted math gains that were
significantly below what their students would have seen if they enrolled in local
traditional public schools instead.
Charter school students on average see a decrease in their academic growth in reading
of .01 standard deviations compared to their traditional school peers. In math, their
learning lags by .03 standard deviations on average. While the magnitude of these
effects is small, they are both statistically significant.

Obviously, there's plenty of individual variation, and states that have more stringent oversight tend to have charters that provide better outcomes than their public schools.