Across the United States, statewide assessments in English language arts and mathematics are federally mandated each school year in grades 3 through 8 and once in high school. The intent is to help educators, policymakers, and parents directly gauge how students and their school systems are performing against state standards. Missing nationwide, however, is any systematic state-level attempt to evaluate students' ongoing progress in grades K-2, the grades that lay the foundation for all later learning. This paper focuses on this lag in K-2 assessment systems and how states can act to address it. We first review a range of assessment types and their utility for supporting learning in the early years of schooling. We then discuss research findings on state K-2 assessment policies that provide insights for other policy leaders to consider as they work to build K-2 assessment systems that effectively help districts and schools support academic success for their youngest students. [For the companion paper, "Kindergarten Readiness Assessments Help Identify Skill Gaps. Policy Perspectives," see ED616031.]