This study aims to determine the contributing factors for early childhood overweight/obesity within the contexts of the child's home, school, and community, and to determine how much each of the ecological contexts contributes to childhood overweight/obesity. The framework was developed from Bronfenbrenner's ecological systems theory. Data for 2,100 children from the Early Childhood Longitudinal Study, Birth Cohort, were used in a series of multilevel modeling analyses. There was significant variation in childhood overweight/obesity by school and community. The majority of variation in childhood overweight/obesity was explained by the child and family factors in addition to school and community factors. Explained variance of childhood overweight/obesity at the school level was 27% and at the community level, 2%. The variance composition at children's family level alone was 71%. Therefore, overweight/obesity prevention efforts should focus primarily on child, family, and school factors and then community factors, to be more effective.