These early years of life are a window of opportunity to lay a strong foundation for a child’s life. Proper health, nutrition, and early stimulation play a critical role for brain development and child well-being. Around the world, poor children under 5 lag behind their more advantaged peers in physical, language, cognitive, and socio-emotional development. Without access to quality ECD, poor children often fall behind their more advantaged peers before they even begin school. As they get older, the gaps widen: they are likely to perform poorly in school, earn less as adults, and engage in risky social behaviors. How do good quality ECD programs work?