Healthy sleep is pivotal for children’s development. Sleep problems (i.e., late bedtime, insufficient sleep, inconsistent sleep patterns) can lead to impaired cognition, behavioral difficulties, decrement in academic performance, and increased risk of developing obesity. Developing healthy sleep habits is especially important for 4–6-year-olds as routines shift when children transition from variable preschool environments to a more structured elementary school setting. However, few studies have harnessed the unique partnerships between teachers and parents in preventing suboptimal child sleep. Therefore, innovative strategies are needed to target healthy sleep development – which may provide benefit across multiple domains ultimately enhancing children’s sleep behavior and daytime functioning in the classroom (e.g., attention, disruptive behavior, prosocial behavior). This project builds upon the Developmental Ecological Transition to Kindergarten model, which posits that supportive alignment across settings (i.e., home and school) is essential for child well-being during transitions into school. Guided by the ORBIT intervention development framework to systematically co-develop a schooland home-based sleep promotion intervention with key stakeholders (kindergarten teachers and parents), this project refines a sleep promotion intervention for kindergarten children via teacher and parent focus groups (Aim 1), tests the intervention strategies for proof-of-concept in a single group design (Aim 2, n=1 school), and pilot tests the feasibility, acceptability, and preliminary signal of effect in a randomized controlled trial (Aim 3, n=4 schools). In Aims 2 and 3, data are collected on feasibility and acceptability (via observation and self-report), child sleep (via wrist-worn accelerometry), and child classroom behavior (via teacher report). The project will provide critical data for the development of a fully powered trial designed to simultaneously improve children’s sleep and social-emotional well-being around the time of school entry.