The Commonwealth Fund has a nearly century-long role in the improvement of children’s health in the United States. A new historical monograph examines the foundation’s more recent efforts to create an integrated model of well-child care capable of addressing children’s cognitive, emotional, and social development needs. The report tells the story of how Commonwealth Fund–supported initiatives—among them, Assuring Better Child Health and Development (ABCD), which emphasized state–federal collaboration—succeeded in convincing parents, payers, providers, and policymakers of the central importance of developmental screening in well-child care. It offers valuable lessons for bringing about change not just in child health, but in other areas where complicated and enduring issues persist.