High-quality early elementary years offer a critical opportunity for child development and academic learning for all children, regardless of their race, family-income level, or culture and home language. All students deserve access to high-quality teachers and leaders trained in how to effectively support their learning. They deserve to attend schools that follow meaningful standards, quality curricula, and that assess and intervene appropriately. Following a high-quality pre-kindergarten (pre-K) experience, the K-3 years set the foundation upon which future learning builds and it must be emphasized that strengthening these years creates opportunities for all. Education leaders and state policymakers have begun to recognize the immense impact a high-quality early learning experience can have on a student's college and career trajectory. In the summer of 2016, Education Commission of the States and its National Partners convened a group of the nation's top experts on K-3 education for a thinkers meeting to reflect on research and practice and then define state policy levers with the greatest potential to impact student outcomes. This K-3 policymakers' guide to action summarizes the top policy components the experts prioritized as essential to building a high-quality state K-3 system. The following are appended: (1) K-3 Thinkers Meeting Participants; and (2) National Partners.