Diane Ravitch has declared that the Obama administration’s policy of expanding the number of charter schools has “no credible basis in research.” This is just plain wrong. And a new study coming out today from Stanford’s Caroline Hoxby demonstrates that she is even more wrong.
I’ve already noted that the highest quality studies — those that avoid bias from the self-selection of students into charter schools either with random-assignment or rigorous instrumental variable research designs — show significant academic benefits for students who attend charter schools instead of traditional public schools. These studies examine the effect of charter schools in Massachusetts, Florida, Chicago, and New York City.
And now add to that pile an updated study from Caroline Hoxby mentioned in today’s WSJ and NYT on New York City charter effects. Students accepted by lottery into one of NYC’s charter schools in kindergarten and remained in a charter school through grade 8 closed the achievement gap with wealthy kids attending schools in Scarsdale entirely in math and two-thirds of the way in reading.
Critics are clinging to a study by Margaret Raymond at CREDO, which shows more mixed results. While that study has the benefit of covering 15 states and DC, it can’t correct for the self-selection of students into charter schools like the highest quality studies linked above. On average, students appear to be drawn to switching to charter schools because they are having trouble in their traditional public school. Simply controlling for those students’ prior achievement and other observed demographic factors doesn’t quite correct for whatever negative factors may have caused students to switch to charters and that may continue to hinder their academic progress. The CREDO study is as good as it can be given its approach, but I would have greater confidence in the consistent findings from several studies in different locations that do control for self-selection into charter schools.
Posted by Jay P. Greene 
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