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« April 28, 2009 | Main | May 13, 2009 »

10 May 2009

Dobbie and Fryer on Charter Schools in the Harlem Children's Zone

David Brooks wrote a column a few days ago about Will Dobbie and Roland Fryer's working paper on the Harlem Children's Zone charter schools, which the authors report dramatically improved students' performance, particularly in math. Looking at the paper, I think it's a nice example of constructing multiple comparisons to assess the effect of a program and to do some disentangling of mechanisms.

The program they study is enrollment in one of the Promise Academy elementary and middle schools in Harlem Children's Zone, a set of schools that offer extended class days, provide incentives for teacher and student performance, and emphasize a "culture of achievement." The authors assess the schools' effect on student test scores by comparing the performance of students at the schools with that of other students. The bulk of the paper is concerned with how to define this group of comparable non-students, and the authors pursue two strategies:

  • First, they examine cases where too many students applied to the school and slots were handed out by lottery; the comparison of lottery winners and non-lottery winners (and the accompanying IV estimate in which attending the school at some point is the treatment) allow them to compare the effect of attending these schools under nearly experimental conditions, at least in years when lotteries were held.
  • Second, they compare students who were age-eligible and not age-eligible for the program, and students who were in the schools' recruitment area vs not in the schools' recruitment area. (This boils down to an IV in which the interaction of cohort and address instruments for attendance at the school.)

The estimated effect is very large, particularly for math. Because the estimates are based on comparisons both within the HCZ and between HCZ and non-HCZ students, the authors can speculate somewhat about the relative importance of the schooling itself vs other aspects of the HCZ: they tentatively suggest that the community aspects must not drive the results, because non-HCZ students did just as well.

Overall I thought it was a nice example of careful comparisons in a non-experimental situation providing useful knowledge. I don't really know this literature, but it seems like a case where good work could have a big impact.

Posted by Andy Eggers at 9:40 AM