Does Helping John Help Sue? Evidence of Spillovers in Education

Does the impact of teachers extend beyond the students in their classroom? Using the natural transitions of students from multiple elementary schools into a single middle school, this paper provides a new method for isolating and quantifying peer spillover effects of teaching and shows that ignoring these spillovers underestimates a teacher's value by at least 30 percent. Because the spillovers also affect teacher value-added estimates, I develop a method of moments estimator of teacher value-added and show that accounting for the spillovers does not have a large impact on the ranking of teachers in New York City. I conclude by showing that the spillovers occur within groups of students who share the same race and gender, which suggests that social networks play a critical role in disseminating the effect.