We use a large-scale randomized experiment to study the impact of augmenting staffing in the world’s largest public early childhood program: India’s Integrated Child Development Services (ICDS). Adding a half-time worker doubled net preschool instructional time and led to 0.29σ and 0.46σ increases in math and language test scores after 18 months for children who remained enrolled in the program. Rates of stunting and severe malnutrition were also lower in the treatment group. A cost-benefit analysis suggests that the benefits of augmenting ICDS staffing are likely to significantly exceed its costs even under conservative assumptions.