Quantifying and Predicting Variation in the Medium-Term Effects of an Oversubscribed Prekindergarten Program

While there is a consensus that attending prekindergarten better prepares children for kindergarten and that effects can last into elementary school, there is little evidence on variation in these effects. To add to this literature, we use data from applicants to oversubscribed schools in Boston Public Schools prekindergarten program to estimate variation in the effects of the program across school sites through the end of third grade. Student outcomes include children's kindergarten-through-second-grade retention, kindergarten-through-third-grade special education placement, and third-grade state test scores. We find statistically significant variation in effects for all student outcomes and we predict this variation with multiple proxies for early elementary school quality. We find that the academic proficiency of third-graders within the schools for which prekindergarten children competed is most strongly associated with prekindergarten program effects. Our findings appear to be driven by the schools themselves and not by student selection in higher-scoring schools, nor by the counterfactual. As preschool programs expand, our study illustrates how impact variation methodology can be used to better understand how to produce larger initial and more lasting child impacts.