The present study examined differences in school readiness skills in the fall of kindergarten between preK attendees and non-attenders (n = 2581) among children in a large, diverse county. Also considered was the extent to which skills associated with pre-K enrollment varied as a function of children’s background characteristics and features oftheir pre-K program. Results revealed pre-K attenders demonstrated better academic and executive function skills in the first months of kindergarten than non-attenders; no consistent differences were detected for teachers’ reports of children’s socioemotional adjustment. Differences in academic skills and self-regulation associated with attendance in pre-K were largest for dual language learners and children from the lowest-income families. Children enrolled in private pre-K programs demonstrated less optimal socioemotional skills at kindergarten entry. (author abstract)