This paper examines whether an expansion in the supply of public preschool crowds out private enrollment, using rich data for municipalities in Brazil from 2000-2006, where federal transfers to local governments change discontinuously with given population thresholds. Results from a regression-discontinuity design reveal that larger federal transfers lead to a significant expansion of local public preschool services, but show no effects on the quantity or quality of private provision. These findings are consistent with a theory in which households differ in willingness to pay for preschool services, and private suppliers optimally adjust prices in response to an expansion of lower-quality, free-of-charge public supply. (author abstract)