This paper studies the effect of the Head Start program on children's achievements in reading and math tests during their first 4 years of schooling after completing the program. Using nationally representative data from the Early Childhood Longitudinal Study, I found large measurement error in the parental reports of Head Start attendance, which is new in the literature. Further I found that after accounting for measurement error and potential selection bias, black Head Start children make significant progress toward third grade, whereas white and Hispanic children reap little gain from the program relative to their peers who were exposed to other types of programs and care. (author abstract)