ABSTRACT Social, emotional, and behavioral (SEB) problems are among the most common chronic disabilities affecting children growing up in urban and rural poverty. They also have implications for children’s school success as they affect essential social-emotional learning skills such as the ability to comply with rules, follow instructions, regulate emotions, and get along with others. These essential skills are first learned before kindergarten (K) entry, in the context of a supportive, responsive, and consistent parenting relationship. To date, universal school-based interventions to improve young children’s social-emotional learning have primarily targeted students and teachers. Yet, parents are the central figures in young children’s lives and they need to be equal partners with schools in promoting SEB skills. This study seeks to improve children’s SEB competence and K readiness by strengthening parent engagement and parenting skills in early childhood education during prekindergarten (PreK). This hybrid Type 2 effectiveness-implementation trial will rigorously evaluate the effects of an evidence-based parenting program, called the Chicago Parent Program (CPP), implemented in PreK on K outcomes in urban and rural Title 1 schools in Maryland. Effectiveness Aims: Using a cluster randomized design (N=30 schools, 840 families; >90% low-income), we will examine the effects of CPP offered universally to Title 1 PreK parents on a) children’s SEB competence, parent engagement, and parenting skills; and b) K readiness, chronic absence, and grade retention in K. We will also examine the mechanisms underlying those effects. Schools will be stratified by rural vs urban district then randomized to experimental (CPP) or control (usual practice) conditions. Data will be collected from multiple informants (parents, teachers, CPP group leaders, school personnel, district administrative data). Implementation Aim: Using the RE-AIM framework and a mixed methods approach, we will assess CPP reach, effectiveness, acceptability, adoption, implementation, cost-effectiveness, and sustainability when offered in different formats (virtual CPP groups vs in-person CPP groups) and contexts (urban vs rural schools). Schools will participate for 2 years with experimental schools offering CPP twice, once in a virtual group format and once in an in-person group format (format counterbalanced), giving us the ability to compare a range of outcomes associated with uptake, acceptability, cost, and sustainability by CPP format in low-resource rural and urban contexts. This study addresses the NICHD priority to test developmentally informed interventions designed to ameliorate early adverse environmental effects on children and optimize their growth, development, and SEB wellbeing.