['To investigate whether aerobic fitness and obesity in school children are associated with standardized test performance.', 'Ethnically diverse (n = 1989) 5th, 7th, and 9th graders attending California schools comprised the sample. Aerobic fitness was determined by a 1-mile run/walk test; body mass index (BMI) was obtained from state-mandated measurements. California standardized test scores were obtained from the school district.', 'Students whose mile run/walk times exceeded California Fitnessgram standards or whose BMI exceeded Centers for Disease Control sex- and age-specific body weight standards scored lower on California standardized math, reading, and language tests than students with desirable BMI status or fitness level, even after controlling for parent education among other covariates. Ethnic differences in standardized test scores were consistent with ethnic differences in obesity status and aerobic fitness. BMI-for-age was no longer a significant multivariate predictor when covariates included fitness level.'] Are low aerobic fitness and obesity associated with lower standardized test scores in children?