Stanford University economist Caroline Hoxby released yesterday an update to her 2007 study of charter schools in New York City.1 In the study, she compares the state examination results of students enrolled in the City’s charter schools (i.e. those students “lotteried-in”) to the results for those students who applied to a charter but were not selected for admission (i.e. the “lotteried-out”). In many respects, this is a good approach as it aims to account for the possibility that charters enroll more motivated families and that it is this motivation, rather than any particular charter school effect, that is the cause of stronger student achievement.
Hoxby’s findings are encouraging: by the third grade, the average charter school student was 5.8 points ahead of the lotteried-out counterpart in math and was 5.3 points ahead in English Language Arts.2 As Hoxby follows students’ achievement from 2001 to 2008, she also finds that the average charter school student gained 3.6 more points each year in math and 2.4 more points each year in ELA. For an average charter student continuously enrolled in grades four through eight, the effect is larger with annual gains of 5.0 points in math and 3.6 in ELA above the performance of the lotteried-out student. (Last year, nine charters enrolled students across all of these grades.)
To put this in some context, Hoxby explains that the difference between a student not meeting standard and meeting standard is about 31 points in math and 44 points in ELA. She also points out that, on average, students in neighboring and affluent Scarsdale typically out-perform students in New York City by 35 to 40 points. In this context, Hoxby claims that the compounded gains for an average student continuously enrolled in third to eighth grade in a charter nearly closes the “Harlem-to-Scarsdale” achievement gap and implies — going outside of her dataset — that the trend will continue.