Background: School environments are important to consider for children's health. This study aims to determine if childhood peer bullying and school connectedness are associated with adolescent adiposity. Methods: A total of 3377 children from the age 9 child interview of the Fragile Families and Child Wellbeing Study had self-reported bullying and school connectedness data at age 9, height and weight measured at ages 9 and 15, and waist circumference was measured during an age 15 home visit. Linear regression models estimated the association between bullying and school connectedness and (1) change in BMI between age 9 and 15, and (2) waist circumference at age 15. Models were stratified by sex. Results: Girls had larger increases in body mass index (BMI) when experiencing low school connectedness, and students that experienced both bullying and low school connectedness had larger increases in BMI. Girls had larger waist circumferences for increased levels of bullying, low connectedness, and experiencing both. Conclusions: School environments may play a role in the development of increased adiposity and there may be gender differences in the types of factors that are important to consider, particularly for central adiposity. Positive and engaging school environments can help support students' development and healthy behaviors.