Preschool interventions are arguably one of the most important elements of support for poor families. Head Start, a federal program for children in low-income families administered through the Department of Health and Human Services, is a case in point. While research shows a range of benefits lasting beyond preschool for participants, evidence of the "fade-out" of cognitive gains of the preschool years and the differential impact of the program on children with different skill levels in the preschool population has prompted debate over its efficacy. Our recent work is the first comprehensive analysis of how modern Head Start impacts vary across the skill distribution in the preschool and early elementary period. We find evidence of a large and positive short-term effect of Head Start, and that cognitive gains are largest at the bottom of the achievement spectrum, particularly among Hispanic children. The results of our study add to the evidence of the success of Head Start in improving the wellbeing of poor children. (author abstract)