BACKGROUND: For many health-related behaviors and outcomes, racial and ethnic disparities among adolescents are well documented, but less is known about health-related disparities during preadolescence. METHODS: We studied 5119 randomly selected public-school fifth-graders and their parents in three metropolitan areas in the United States. We examined differences among black, Latino, and white children on 16 measures, including witnessing of violence, peer victimization, perpetration of aggression, seat-belt use, bike-helmet use, substance use, discrimination, terrorism worries, vigorous exercise, obesity, and self-rated health status and psychological and physical quality of life. We tested potential mediators of racial and ethnic disparities (i.e., sociodemographic characteristics and the child's school) using partially adjusted models. RESULTS: There were significant differences between black children and white children for all 16 measures and between Latino children and white children for 12 of 16 measures, although adjusted analyses reduced many of these disparities. For example, in unadjusted analysis, the rate of witnessing a threat or injury with a gun was higher among blacks (20%) and Latinos (11%) than among whites (5%), and the number of days per week on which the student performed vigorous exercise was lower among blacks (3.56 days) and Latinos (3.77 days) than among whites (4.33 days) (P<0.001 for all comparisons). After statistical adjustment, these differences were reduced by about half between blacks and whites and were eliminated between Latinos and whites. Household income, household highest education level, and the child's school were the most substantial mediators of racial and ethnic disparities. CONCLUSIONS: We found that harmful health behaviors, experiences, and outcomes were more common among black children and Latino children than among white children. Adjustment for socioeconomic status and the child's school substantially reduced most of these differences. Interventions that address potentially detrimental consequences of low socioeconomic status and adverse school environments may help reduce racial and ethnic differences in child health. (Funded by the Centers for Disease Control and Prevention.) Copyright © 2012 Massachusetts Medical Society.