Early childhood programs are heralded as a way to improve children’s health and educational outcomes. However, few studies in developing countries calculate the effectiveness of quality early childhood interventions. Even fewer estimate the associated costs of such interventions. The study here looks at the costs and effectiveness of a clusterrandomized effectiveness trial on children from birth to 24 months in rural Sindh, Pakistan. Responsive stimulation and/or enhanced nutrition interventions were integrated in the Lady HealthWorker program in Pakistan. Outcomes suggest that childrenwho receive responsive stimulation had significantly better development outcomes at 24months than those who only received enhanced nutrition intervention. A cost-effectiveness analysis of the results verifies that early childhood interventions that include responsive stimulation aremore cost effective than a nutrition intervention alone in promoting children’s early development. Costs of a responsive stimulation intervention integrated in an existing community-based service providing basic health and nutrition care is approximately US$4 per month per child. We discuss these findings and make recommendations about scaling up and costs for future early child development programs.