The purpose of the current study is to examine whether the duration of Head Start participation is associated with a child's weight and height. Method: The study employs a secondary analysis of 2,690 Head Start participants, 891 who entered at age 3 and enrolled for 1 year, 1,125 who entered at age 4 and stayed for 1 year, and 674 who entered at age 3 and stayed for 2 years. A logistic regression correctly classified the obesity probability (82.8%). Results: Early entry age and a longer duration in Head Start is associated with a lower obesity rate. Conclusion: Head Start should accept younger children and have them stay for a longer duration, particularly for children in high risk families. (author abstract)