Summary Young children who enter school without sufficient social and emotional learning (SEL) skills may have a hard time learning. Yet early childhood educators say they don't get enough training to effectively help children develop such skills. In this article, Megan McClelland, Shauna Tominey, Sara Schmitt, and Robert Duncan examine the theory and science behind early childhood SEL interventions. Reviewing evaluation results, they find that several interventions are promising, though we need to know more about how and why their results vary for different groups of children. Three strategies appear to make interventions more successful, the authors write. First, many effective SEL interventions include training or professional development for early childhood teachers; some also emphasize building teachers' own SEL skills. Second, effective interventions embed direct instruction and practice of targeted skills into daily activities, giving children repeated opportunities to practice SEL skills in different contexts; it's best if these activities grow more complex over time. Third, effective interventions engage children's families, so that kids have a chance to work on their SEL skills both at school and at home. Family components may include teaching adults how to help children build SEL skills or teaching adults themselves how to practice and model such skills. Are early childhood SEL interventions cost-effective? The short answer is that it's too soon to be sure. We won't know how the costs and benefits stack up without further research that follows participants into later childhood and adulthood. In this context, we particularly need to understand how the long-term benefits of shorter, less intensive, and less costly programs compare to the benefits of more intensive and costlier ones. www. futureofchildren. org To be ready to enter school, young children need social and emotional learning (SEL) skills such as getting along with others, paying attention, following directions, and managing emotions. Yet teachers report that many children enter school without these skills, which can make it challenging for them to learn. (1) And early childhood educators often feel that they don't receive enough training to effectively help children develop SEL skills. (2) In response, policymakers and practitioners have focused on SEL, and interventions that promote SEL skills for young children have proliferated. SEL interventions take many approaches, and their very diversity makes it challenging to determine which components and approaches are most effective. To ensure that all children have the skills to thrive, we need to pinpoint what works under what conditions and with what populations. In this article, we examine the science behind SEL interventions. We start by clarifying key terms related to SEL skills and reviewing the approaches used in current early childhood SEL interventions. We discuss the theories that guide these interventions, as well as results from intervention studies, including a look at how results vary for different groups of children. Next we examine intervention characteristics that relate to SEL growth and review the potential financial and societal benefit of SEL interventions. We conclude by discussing the limitations of current SEL interventions and making recommendations for research and policy. Social and Emotional Learning: Key Terms Social and emotional learning (SEL) refers to a broad range of social, emotional, and behavioral skills for children. We highlight three main components of SEL skills: emotional processes, social/interpersonal skills, and cognitive regulation. (3) The first component, emotional processes, encompasses the skills children need to manage their emotions effectively and recognize the emotions of others. Emotional processes include skills such as emotion knowledge (the ability to recognize and label emotions accurately), emotion regulation (managing emotions and controlling how and when we express them), perspective taking, and empathy. …