BACKGROUND: Previous studies have demonstrated gender-related differences in body composition, physical activity, and diet. This observational study assesses gender variance in independent predictors for obesity to determine targeted areas for intervention. METHODS: Data from 1714 sixth-grade students enrolled in Project Healthy Schools were compared by using health behaviors and physiologic markers (lipids, random glucose, blood pressure, and resting and recovery heart rates). Students were stratified by gender and obesity (BMI ≥95th percentile by age and gender). Physiologic markers and behaviors were compared by using χ2 analysis. Univariate associations with P <.10 were included in a stepwise logistic regression model to determine independent predictors for obesity by gender. RESULTS: Nonobese students (both boys and girls) showed significantly healthier physiologic parameters compared with their obese counterparts. Two behaviors independently correlated with obesity in both boys and girls: regularly eating school lunches (odds ratio [OR] 1.29, 95% confidence interval [CI] 1.01-1.64; OR 1.27, 95% CI 1.00-1.62, respectively) and watching ≥2 hours of television per day (OR 1.19, 95% CI 1.07-1.32; OR 1.19, 95% CI 1.06-1.34, respectively). Vigorous physical activity and involvement in school sports teams appeared to be protective against obesity in boys (OR 0.90, 95% CI 0.82-0.98; OR 0.77, 95% CI 0.64-0.94, respectively), whereas milk consumption appeared protective in girls (OR 0.81, 95% CI 0.67-0.98). CONCLUSIONS: Among middle-school children, we observed genderrelated differences in factors associated with obesity. Additional research is warranted to determine the beneficial impact of improving school lunches and decreasing screen time, while improving our understanding of gender-related differences in milk consumption and physical activities in relation to BMI. Copyright © 2013 by the American Academy of Pediatrics.