There is a growing consensus in education that schools can and should attend to students' social-emotional development. Emerging research and popular texts indicate that students' mindsets, beliefs, dispositions, emotions, and behaviors can advance outcomes such as college readiness, career success, mental health, and relationships. Despite this growing awareness, many districts and schools are still struggling to implement strategies that develop students' social-emotional skills. This report seeks to fill this gap by examining the social-emotional learning (SEL) practices in one network of California school districts--the CORE districts--that are working together to measure and improve SEL. We focus on schools with strong student-reported data on SEL outcomes, particularly for African American and Latinx students. To support the sharing of promising practices in this emerging field, we investigate how district and school leaders and educators interpret SEL and support it in and outside of the school day. [For the related brief, see ED591087.]