The central message of this report is that principals across the United States understand how fundamental social and emotional learning (SEL) is to the development of students and their success in and out of school, but they need more guidance, training, and support to make solid and effective school-wide implementation a reality. Principals understand that SEL competencies are teachable, believe they should be developed in all students, and know that young people equipped with SEL skills will become better students now and better adults in the future. In today's environment of increasingly demanding jobs and the fraying of American communities, nothing could be more important than to foster, teach, and promote the competencies of self-awareness, self-management, social awareness, relationship skills, and responsible decision-making. Some call it empathy, discipline, character, collaborative problem solving, or other names--but regardless of the name, they are the attitudes and skills that provide the glue of a functioning society, robust economy, and vibrant democracy. Most principals see how SEL boosts student academic achievement, but they want more evidence of those impacts to strengthen the case for action. Although support among principals for embedding SEL in the culture and classrooms of schools is high, implementation varies widely across schools with about one in three principals implementing it school-wide, and only one in four meeting benchmarks for high-quality implementation. Encouragingly, when principals and teachers attempting to implement SEL are well supported by their district leadership, they have better outcomes, and when state policymakers back district leaders, the results are even more pronounced. These and other findings come from a nationally representative survey of 884 Pre-K to 12 public school principals and interviews with 16 superintendents and 10 district-level research and evaluation specialists representing diverse school districts and with varying levels of experience in implementing SEL programming. Despite representing different grade spans, student populations, and geographic areas, the administrators in this report see the potential in social and emotional learning and provide key insights into the factors that can either slow SEL implementation at the school and district levels or help it grow and flourish. This strong support for SEL among our nation's principals builds on similar levels of support from teachers across the United States, as reported in the 2013 report, "The Missing Piece". While our educational leaders and practitioners see the value of SEL, they need support, resources, and tools to help them fully implement systemic SEL initiatives that can improve students' SEL knowledge, skills, and attitudes, as well as their college, career, and life readiness.