Preschool parent interventions may produce downstream benefits if initial intervention gains are sustained and improve later socialization experiences. This study explored associations between initial effects of the REDI (Research-based Developmentally Informed) Parent program and later benefits. A randomized trial involving 200 Head Start children (55% European-American, 26% African American, 19% Latino, 56% male, M[subscript age] = 4.45 years) produced kindergarten gains in parenting and child skills. Four years later, sustained effects were evident in areas of academic performance and social-emotional competence at school and new benefits emerged at home. Initial gains in child academic and social-emotional domains mediated sustained gains within the same domains. In addition, initial gains in parent-child conversations, parent academic expectations, and child social-emotional skills mediated later reductions in parenting stress and child problems at home. Parent-focused preschool interventions may not only promote sustained improvements in child school adjustment but may also foster better family functioning over time. [This paper was published in "Journal of Applied Developmental Psychology" v64 Article 101058 2019.]