Energy balance–related behavior on schooldays and beliefs about school-based interventions may differ between students in different educational levels, sexes, and BMI (body mass index) categories. In Zwolle (the Netherlands), 1,084 adolescents (13-15 years) at 9 secondary schools completed a questionnaire. Overweight prevalence (boys 18.1%, girls 19.3%) increased with decreasing educational level, especially in boys. Girls reported healthier behavior than boys regarding daily consumption of fruit (35% vs. 29%), vegetables (58% vs. 48%), ≤1 snack/candy (36% vs. 26%), ≤3 glasses of sugared drinks (80% vs. 73%; all p < .05). Unhealthier dietary behaviors were associated with lower educational level, except for eating sugary and savory snacks. Snacks and sugared drinks consumed at school were mostly brought from home (61.6% and 68.5%, respectively). Overweight students reported less frequent consumption of daily breakfast, snacks, and sugared drinks than nonoverweight students. Of all students, 40% spent ≥1 hour per day cycling to school. Lower educational level students reported less organized sports activities than higher level students, but more outside play and other activities. Overweight was associated with cycling to school (boys) and participating in organized sports (girls). More girls than boys were interested in lessons about healthy nutrition (44.4% vs. 31.7%). To stimulate physical activity, boys suggested more physical education classes (63%), girls advised more variation (47%) and choice (43%). A healthy school canteen (57%) and offering free fruit (67%) were suggested as promising interventions to stimulate healthy behavior. Educational and environmental interventions to tackle unhealthy dietary and physical activity behavior should be developed in collaboration with parents and tailored to educational level and gender.