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). Results suggest that the Pre-K experience positively affects these children in a variety of domains, including language (d = 0.41-0.74), early literacy (d = 0.99-1.36), and early mathematical problem-solving (d = 0.54-0.71), a pattern of benefits which is consistent with the targets of the Pre-K curriculum in this jurisdiction. However, effects were not robust for executive functioning, a domain that has had less empirical attention in Pre-K evaluations. Importantly, our study also includes several enhancements to the Pre-K RD design that are recommended by experts but that have not been used widely in this literature. Thus, this study contributes both to the literature on the benefits for children, from largely minoritized, low-income backgrounds, of preschool education implemented at scale and to the methodological literature on RD evaluations of Pre-K programs.