Summary There's a strong case for making social and emotional learning (SEL) skills and competencies a central feature of elementary school. Children who master SEL skills get along better with others, do better in school, and have more successful careers and better mental and physical health as adults. But evidence from the most rigorous studies of elementary-school SEL programs is ambiguous. Some studies find few or no effects, while others find important and meaningful effects. Or studies find effects for some groups of students but not for others. What causes such variation isn't clear, making it hard to interpret and act on the evidence. What are the sources of variation in the impacts of SEL programs designed for the elementary years? To find out, Stephanie Jones, Sophie Barnes, Rebecca Bailey, and Emily Doolittle examine how the theories of change behind 11 widely used school-based SEL interventions align with the way those interventions measure outcomes. Their central conclusion is that what appears to be variation in impacts may instead stem from imprecise program targets misaligned with too-general measures of outcomes. That is to say, program evaluations often fail to measure whether students have mastered the precise skills the programs seek to impart. The authors make three recommendations for policy makers, practitioners, and researchers. The first is that we should focus more on outcomes at the teacher and classroom level, because teachers' own social-emotional competency and the quality of the classroom environment can have a huge effect on students' SEL. Second, because the elementary years span a great many developmental and environmental transitions, SEL programs should take care to focus on the skills appropriate to each grade and age, rather than taking a one-size-fits-all approach. Third, they write, measurement of SEL skills among children in this age range should grow narrower in focus but broader in context and depth. www.futureofchildren.org Research has shown that during the elementary school years, social and emotional skills are related to positive academic, social, and mental health outcomes. For example, correlational studies show that classrooms function more effectively and student learning increases when children can focus their attention, manage negative emotions, navigate relationships with peers and adults, and persist in the face of difficulty. (1) Children who effectively manage their thinking, attention, and behavior are also more likely to have better grades and higher standardized test scores. (2) Children with strong social skills are more likely to make and sustain friendships, initiate positive relationships with teachers, participate in classroom activities, and be positively engaged in learning. (3) Indeed, social and emotional skills in childhood have been tied to important life outcomes 20 to 30 years later, including job and financial security, as well as physical and mental health. (4) This compelling evidence suggests that there's a strong case for making such non-academic skills and competencies a central feature of schooling, both because of their intrinsic value to society and, from a pragmatic standpoint, because they may help to reduce achievement and behavior gaps and mitigate exposure to stress. (5) But what do we know about efforts designed to improve and support social and emotional skills in the elementary years? The evidence from gold-standard studies--in which one group is randomly assigned to receive an intervention while another is not--is ambiguous. What works, for whom it works, and under what conditions often varies. For example, we've seen largescale national studies that find small or no effects from interventions designed for the elementary school years, and many individual studies that find important and meaningful effects. (6) What causes such variation isn't clear, making it hard to interpret and act on the evidence. …