Extensive research on preschool quality has consistently identified the use of a formal curriculum as an important component of programs that promote young children’s learning. Both Head Start and the National Association for the Education of Young Children (NAEYC) identify research-based curriculum, grounded in knowledge of child development, as a core element of high-quality programs. Yet no consensus exists on what constitutes curricular quality. To help fill this guidance gap, the National Academies of Sciences, Engineering, and Medicine (NASEM) has launched a study that will articulate a consensus definition of curriculum quality for children ages three to five.