Background paper prepared for the 2016 Global Education Monitoring ReportThe proposed education goal for the post-2015 sustainable development agenda includes a target focused on ensuring children begin formal schooling developmentally on track and “ready for primary school.” What does it mean for a child at school entry to be developmentally on track, and how should it be measured? This paper reviews issues and approaches to measurement of young children’s development in light of the education target on early childhood development. Basic principles of child development with implications for measurement are described, along with issues in accurately capturing the complex nature of early development with feasible, cost-effective measures. Analyses of some of the most commonly-used regional and global measures of young children’s development are described, with emphasis on identifying the policy relevance, feasibility, and methodologies that influence their potential usefulness for measuring national, regional or global progress towards proposed global education goals. Finally, directions for measuring early childhood development and learning in the proposed agenda are outlined