With a large volume of literature pointing to the beneficial impact of pre-kindergarten, researchers, educators, and policymakers are now raising questions about what works for whom, under what conditions, as well as conducting cost-benefit analyses of such endeavors. However, few studies exist on the differential and contextual effects of these programs, creating opportunities for new research in this area. This paper addresses this issue by reporting on the short-term effects of a state-funded pre-kindergarten program, including the potential differential effects among students of color and students from lower income families. Using data from the Connecticut School Readiness Program (CSRP), we use a regression discontinuity design to examine the causal impact of attending the CSRP on average, and by race and income across four different outcomes (reading, oral language, vocabulary, and mathematics). We find that, in the aggregate, attending the CSRP provided the strongest and most consistent outcomes in reading and mathematics. However, heterogeneity analyses indicate variation in impact. The magnitude and significance of reading and mathematics effects were positive but smaller for Black children. Null effects were detected for Latinx students. There was suggestive evidence that mathematics impacts may be smaller for students from low-income families, while reading impacts are uniformly positive irrespective of family income. Possible explanations for differential impact findings are explored. (author abstract)