Social and emotional learning (SEL) is having a moment. After years of being neglected for an agenda heavily focused on test scores, the pendulum is swinging back toward the whole child. The 2015 reauthorization of the Elementary and Secondary Education Act asks states to develop at least one metric, outside reading and math scores, to measure school quality. In a field in which it is often claimed that nothing works, SEL has a track record of verifiable, if modest, success. SEL has succeeded by meeting real demand for its services; setting modest and specific goals; matching the needed support, materials, and training to these goals; and avoiding a one-size-fits-all mentality. The most promising approaches integrate academics and SEL schoolwide, rather than making SEL a set-aside program. Meanwhile, policymakers should be wary of mandating SEL; there is no faster way to lose support for an initiative than to require that everyone take part. The author suggests that those who want to spread the movement need to eschew mandates and use other forces for social change--education, movement building, persuasion, evidence, and more--to gradually and sustainably spread SEL across the nation's many schools.