This research report from MDRC, Building Knowledge to Improve Social Policy examines the effects of early social-emotional learning (SEL) programs on students’ academic and behavioral outcomes through middle school. Although research on SEL programs show their value in improving students’ academic performance, social-emotional skills, and attitudes towards school and self, the report acknowledges that most studies examined effects for less than one year. Bridging the gap of limited evidence about SEL programs’ long-term impacts, this research study conducted a randomized trial on INSIGHTS into Children’s Temperament, a 2-year intervention implemented in kindergarten and 1st grade. The study found targeting SEL support in high-poverty schools may make intervention more effective, but that early SEL interventions alone may be insufficient for lasting effects. The report recommends ongoing support, grade-aligned learning and targeted interventions that consider students’ backgrounds. Educators, school administrators, and district leaders may find this resource useful in the implementation and improvement of SEL programs and interventions.