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Maimonides Rule Redux

Maimonides Rule Redux: Does Class Size Affect Student Achievement?

New Findings, School Reform, June 2017

We use the discontinuous function of enrollment known as Maimonides Rule as an instrument for class size in large Israeli samples from 2002-2011. As in the 1991 data analyzed by Angrist and Lavy (1999), Maimonides Rule still has a strong first stage. In contrast with the earlier Israeli estimates, however, Maimonides-based instrumental variables estimates using more recent data show no effect of class size on achievement. The new data also reveal substantial enrollment sorting near Maimonides cutoffs, with too many schools having enrollment values that just barely produce an extra class. A modified rule that uses data on students’ birthdays to compute statutory enrollment in the absence of enrollment manipulation also generates a precisely estimated zero. In older data, the original Maimonides Rule is unrelated to socioeconomic characteristics, while in more recent data, the original rule is unrelated to socioeconomic characteristics conditional on a few controls. Enrollment manipulation therefore appears to be innocuous: neither the original negative effects nor the recent data zeros seem likely to be manipulation artifacts.