Following a high-quality early care and pre-K experience, the kindergarten-through-third-grade years set the foundation upon which future learning builds; and strengthening this continuum creates opportunities for later success. Key components of a quality experience in K-3 include school readiness and transitions, kindergarten requirements, educator quality, prevention, intervention and assessments, and social and emotional learning and mental health. Education Commission of the States researched the policies and regulations that guide these key components in all 50 states to provide this comprehensive resource and many others. The data in this document show that at least 35 states have statutes or regulations requiring pre-service and in-services training and professional development on social and emotional learning. This may be included in teacher preparation program requirements, endorsement qualifications or teaching standards, as well as annual training requirements to maintain a teaching license or certification. Additionally, several states have adopted the Council of Chief State School Officers Model Core Teaching Standards which include social and emotional concepts.