Adolescence represents a high-risk period for eating disorder development, and there is great need for effective prevention programs targeted at this population. The Body Project, a dissonance-based eating disorder prevention program, has robust literature showing reductions in body dissatisfaction and eating disorder symptoms. However, many additional factors (i.e., comorbid symptoms, transdiagnostic factors) have not yet been examined in relation to the Body Project. Additionally, there is little known about how to most effectively and broadly disseminate this intervention. The current study (N = 332 adolescents) examines eating disorder symptoms, comorbidities, and transdiagnostic risk factors pre- and post-Body Project and at 1-month follow-up. This study is the first examination of the effectiveness of the Body Project implemented within school programming in southern, all-female high schools. Social appearance anxiety, physical and social anxiety sensitivity, rumination, worry, perfectionism, and guilt, but not depression, cognitive anxiety sensitivity, shame, or exercise dependence, decreased pre- to post-intervention and/or 1-month follow-up. These results support the effectiveness of the Body Project in addressing eating disorder symptoms and suggest it may aid in the prevention of comorbid conditions. Additionally, the effectiveness of the intervention was comparable to past investigations, supporting its use in schools across the United States.