Funded by the Office of Planning, Research and Evaluation in the Administration for Children and Families, this new study will examine how different dimensions and thresholds of quality in early childhood classrooms relate to children’s developmental outcomes. In this study, we will unpack the “black box” of quality and its drivers in early care and education settings with a rigorous experimental design. The projected sample for the study will include approximately 150 programs and 2,000 children across multiple localities. It is a 5-year project that begins with a design phase, before a small pilot test in approximately 24 programs, and then a full-scale study. MDRC is the prime contractor. MEF Associates is leading site recruitment and will be involved in all phases of project implementation.