In this brief, Pennsylvania State University summarises what is known about effective preschool social-emotional learning (SEL) programs and practices based on recent research studies. The studies presented in the brief support the use of SEL programs in preschool, with evidence of positive impacts on children’s development of SEL skills, their engagement with learning, interpersonal relationships and educational achievement. The paper identifies critical factors for success, such as supportive teacher-child interactions and effective engagement with parents.