Recently, practitioners, researchers, and policymakers have placed greater emphasis on early childhood education (ECE) teachers' use of ongoing assessments to track children's progress and tailor instruction to each child's unique strengths, needs, and interests. Ongoing child assessment involves repeated assessments and observations of a child's performance and progress over time. Using ongoing child assessment to tailor or individualize instruction for each child is considered a best practice in early education programs and is a requirement in the Head Start Performance Standards. To learn more about the use of ongoing assessment in early education, the Office of Planning, Research & Evaluation funded a project in fall 2012 to explore how teachers use children's data to tailor instruction for each child. The project's goals are to (1) review the existing literature and develop a conceptual framework of ECE teachers use of ongoing child assessment to individualize instruction and (2) create a measurement tool to examine this process further. This brief summarizes findings from the review of the literature on ongoing assessment in early childhood, including what we know, what we still need to learn, and some recommended practices for using assessments to support children's learning and development. (author abstract)