Objective: Study the effects of multiple exercise and nutritional educational interventions on adverse body mass index (BMI) gain of BMI sub-groups of predominately Hispanic six through eight year-old children at high risk for obesity. Design and Methods: BMI and demographic data were recorded at baseline and six months later in 749 first and second grade public school children at four elementary schools. Two schools (intervention group) received 150 min of extra physical education classes, weekly cooking classes, a structured nutritional curriculum, and parental counseling. BMI changes were calculated for each student and compared by BMI percentile subgroups using the two tailed T-test. Results: No statistical BMI differences occurred between intervention and control group children below the 25th percentile. Significance differences in BMI gain were noted from the 25th to the 50th percentile (P 5 0.027), 50th-75th percentile (P 5 0.045), and 75th-95th percentile (P 5 0.00007), but not for the 95th-98th percentile (P 5 0.288), 98th and above (P 5 0.223), or both obese groups combined (P 5 0.085). Conclusions: Nutritional education and exercise can prevent but not treat obesity in predominately Hispanic first and second grade children. BMI subgroups should be studied to avoid masking differing outcomes of obese and nonobese children.