The theoretical case for universal pre-primary education is strong. However, the empirical foundation is less so. In this paper, we contribute to the empirical case by investigating the effect of a large expansion of universal pre-primary education on subsequent primary school performance in Argentina. We estimate that one year of pre-primary school increases average third grade test scores by 8% of a mean or by 23% of the standard deviation of the distribution of test scores. We also find that pre-primary school attendance positively affects student's selfcontrol in the third grade as measured by behaviors such as attention, effort, class participation, and discipline.