OBJECTIVE: In this research we aimed to evaluate the efficacy of a theoretically derived school-based body image intervention for young adolescent girls. METHOD: Participants were 194, female Grade 7 students from two Catholic Secondary Schools in Melbourne, Australia. One school was allocated to the intervention group and the other school was allocated to the control group. The intervention group participated in three 50-min body image intervention sessions, while the control group received their usual classes. All participants completed baseline, post-intervention and 3-month follow-up questionnaires. RESULTS: The intervention group reported significantly more positive outcomes than the control group on measures of intervention topic knowledge, risk factors for body dissatisfaction, body image, dietary restraint and self-esteem, at post-intervention and follow-up. DISCUSSION: This study provides support for the efficacy of a theoretically derived school-based body image intervention with adolescent girls.