Substantial research has documented that Pre-Kindergarten (Pre-K) programs have important benefits for the school readiness of young children, especially those from low-income backgrounds. Recent studies in this arena have taken advantage of the Regression Discontinuity (RD) design to evaluate the impacts of Pre-K, due to ethical and pragmatic issues. In this study, we use an RD approach to evaluate the effects of the Preschool Development Program in Baltimore, MD, a city with a large proportion of families from socioeconomically and racially marginalized backgrounds who contend with multiple environmental risks. We compared a group of children who had received Pre-K (n = 554) to a group who had not yet participated in Pre-K (n = 542). (author abstract)