Dissonance-based body image interventions are among the most effective interventions for adolescent girls. However, dissemination of these interventions remains challenging. In addition, the emerging field of positive body image suggests that interventions should promote body appreciation as well as reduce pathology. The current study examines whether undergraduate students can effectively deliver a dissonance-based intervention to secondary school girls. In addition, it examines whether this intervention can increase body appreciation. Sixty-two adolescent girls were randomly allocated to the intervention or control condition. In the intervention group, body dissatisfaction was significantly reduced and body appreciation was significantly improved from pre- to post-intervention. There were no changes in body dissatisfaction or body appreciation in the control group. There was a reduction in thin-ideal internalization for all participants. These preliminary findings suggest that undergraduate students can be effective interventionists for dissonance-based programs in schools and dissonance-based interventions can promote body appreciation.