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 19 states plus the District of Columbia require children to attend kindergarten based on state statutes or regulations. Of those that require children to attend kindergarten, guidance is provided to articulate that children must attend or pass an academic readiness screening to enter grade one. States that do not require kindergarten attendance have been identified by their compulsory age requirements or specific indication in statutes and regulations.