This study examines the efficacy of ParentCorps among 4-year-old children (N = 171) enrolled in prekindergarten in schools in a large urban school district. ParentCorps includes a series of 13 group sessions for parents and children held at the school during early evening hours and facilitated by teachers and mental health professionals. ParentCorps resulted in significant benefits on effective parenting practices and teacher ratings of child behavior problems in school. Intervention effects were of similar magnitude for families at different levels of risk and for Black and Latino families. The number of sessions attended was related to improvements in parenting. Study findings support investment in and further study of school-based family interventions for children from underserved, urban communities.