Introduction: The aim of this study was to evaluate the school-based "My Body and I" program which was designed to help girls and boys to cope better with inevitable pubertal body changes. Method: Using a pre-post treatment-control design with 25 treatment and 17 control classes from schools in Germany and France (484 boys, 485 girls; mean age: 10.5 years), changes were measured between a pretest and a posttest. Results: Compared with the control condition, students in the treatment condition exhibited a significant increase in knowledge (effect size = 0.89), a decrease in body dissatisfaction (ES = 0.12), body shape concerns (ES = 0.11), and a shift away from the thin ideal (ES = 0.13). Discussion and Conclusion: The findings suggest that "My Body and I" is an effective primary prevention program reducing the risk for body dissatisfaction among 4th and 5th graders.