There are hundreds of studies of the effects of social-emotional learning (SEL) programs, but only a small fraction of them provide causal evidence on the impacts of school-based “universal” (non- targeted) programs on student achievement.The most reliable studies of universal school-based SEL programs—those employing randomized controlled trials and large samples of students—showed positive effects of SEL on student achievement, on average, but there is substantial variation in the estimated impacts across studies. On average, SEL programs implemented in elementary schools tended to be more effective than those employed in secondary schools. However, impacts do not appear to vary consistently with the intensity of program delivery or with the economic status of the students a school serves. There are a variety of popular SEL programs, but the evidence base on the effects of any particular program on student outcomes is thin. The most frequently studied programs tend to garner mixed results.