First in the Class? Age and the Education Production Function

We estimate the effects of having more mature peers using data from an experiment where children of the same age were randomly assigned to different kindergarten classrooms. Exploiting this experimental variation in conjunction with variation in expected kindergarten entry age to account for negative selection of older school entrants, we find that exposure to more mature kindergarten classmates raises test scores up to eight years after kindergarten, and may reduce the incidence of grade retention and increase the probability of taking a college-entry exam. These findings are consistent with broader peer effects literature documenting positive spillovers from having higher-scoring peers and suggest that - contrary to much academic and popular discussion of school entry age - being old relative to one's peers is not beneficial.