The objective of this study was to evaluate the effects of a school-based exercise program on posture, trunk range of motion and musculoskeletal pain in schoolchildren. This study was a Randomized controlled trial. The hypothesis was that the exercise group would have the postural deviations corrected, would have the trunk range of motion increased and would have the prevalence of pain decreased, while the control group would have not. Three schools from Brazil participated. The students that have been included (n=300) were randomly allocated to experimental (EG) or control group (CG). The intervention for EG consisted in a program based on stretching and strengthening exercises, applied twice a week, for eight weeks, with group sessions of 50 minutes. CG did not perform any intervention. Qualitative and quantitative postural evaluation (PAS/SAPO), musculoskeletal pain (self-report) and trunk mobility were collected.