The Effect of Class Size on Teacher Attrition: Evidence from Class Size Reduction Policies in New York State

Starting in 1999, New York State implemented class size reduction policies targeted at early elementary grades, but due to funding limitations, most schools reduced class size in some grades and not others. I use class size variation within a school induced by the policies to construct instrumental variable estimates of the effect of class size on teacher attrition. Teachers with smaller classes were not significantly less likely to leave schools in the full sample of districts but were less likely to leave a school in districts that targeted the same grade across schools. District-wide class size reduction policies were more likely to persist in the same grade in the next year, suggesting that teacher expectations of continued smaller classes played a role in their decision whether or not to leave a school. A decrease in class size from 23 to 20 students (a decrease of one standard deviation) under a district-wide policy decreases the probability that a teacher leaves a school by 4.2 percentage points.