This study examined the effects of the Head Start Research-Based, Developmentally Informed (REDI) preschool intervention on growth in children’s executive-function (EF) skills from preschool through third grade. Across 25 Head Start centers, each of 44 classrooms was randomly assigned either to an intervention group, which received enhanced social-emotional and language-literacy components, or to a “usual-practice” control group. Four-year-old children (N = 356; 25% African American, 17% Latino, 58% European American; 54% girls) were followed for 5 years, and EF skills were assessed annually. Latent-class growth analysis identified high, moderate, and low developmental EF trajectories. For children with low EF trajectories, the intervention improved EF scores in third grade significantly more (d = 0.58) than in the control group. Children who received the intervention also demonstrated better academic outcomes in third grade than children who did not. Poverty often delays EF development; enriching the Head Start program with an evidence-based curriculum and teaching strategies can reduce early deficits and thereby facilitate school success. (author abstract)