ABSTRACTBACKGROUNDSchool‐level socioeconomic status (SES) influences on adolescents' lifestyle behaviors is understudied. We examined how school‐level SES and sex influence adolescents' health‐related lifestyle behaviors and intentions.METHODSGrade 8 students aged 13‐14 years completed an online questionnaire regarding their sociodemographic characteristics, dietary behaviors, physical activity participation and recreational screen‐time, and intentions regarding these behaviors. School‐level SES, based on an Index of Community Socio‐Educational Advantage (ICSEA), was categorized as low or high. Generalized estimating equations estimated individual‐level summary statistics, adjusted for clustering.RESULTSStudents (N = 2538; response rate = 79%) from 23 high schools (low ICSEA = 16) participated. Compared with low ICSEA students, high ICSEA students were more likely to report eating breakfast daily (OR 1.9 [95% CI 1.5, 2.4]), not drinking sugar‐sweetened beverages (SSBs) daily (2.9 [1.9, 4.3]), and were more likely to have intentions to eat breakfast (1.8 [1.3, 2.3]) and ≥ 5 vegetable serves (1.2 [1.0, 1.5]) daily. Boys were more likely than girls to meet recommendations for breakfast eating, vegetable intake, moderate‐to‐vigorous physical activity and screen‐time, but boys were less likely to meet recommendations regarding SSB intake.CONCLUSIONSStudents from low ICSEA schools would benefit from additional support to improve dietary‐related behaviors and intentions. More research is required to identify what targeted approaches will address sex differences in adolescents' lifestyle behaviors.