Garcia-Hermoso, AAGarcia-HermosoFernandez-Vergara, OOFernandez-VergaraChacana-Canas, CesarCesarChacana-CanasGonzalez-Calderon, NicoleNicoleGonzalez-CalderonHormazabal-Aguayo, IgnacioIgnacioHormazabal-AguayoRussell-Guzman, JavierJavierRussell-GuzmanVicencio-Rojas, FranciscaFranciscaVicencio-Rojasdel Pozo-Cruz, BorjaBorjadel Pozo-Cruz2025-04-232025-04-23201910.1016/j.ijchp.2019.05.001https://sic.vriic.usach.cl/entities/publication/b867b995-0537-4f38-88c1-157b76cc1242Background/Objective: To test the effectiveness of an 8-week before-school physical activity program to reduce bullying victimization among a group of socially disadvantaged children in the Active-Start study. Method: A non-blinded randomized controlled trial was conducted in three public schools classified as highly vulnerable and located in a deprived area of Santiago (Chile). A total of 5 classes participated, totaling 170 fourth grade children. The intervention was delivered before starting the first school-class (8:00–8:30 a.m.). The program lasted for 8 weeks. Primary outcome measurement on bullying victimization was assessed by the CUBE questionnaire at baseline and post-intervention. Results: There was a statistically significant reduction in the probability of suffering physical bullying (OR= 0.18, 95% CI, 0.04-0.82; p= .027) and verbal bullying (OR=0.13, 95% CI, 0.02-0.97; p= .046) after the 8-week program. Conclusions: Participation in an 8-week before-school physical activity intervention implemented in schools located in a disadvantaged district in Santiago (Chile) resulted in lower levels of bullying victimization among study participants. The Active-Start program may be a feasible and potentially scalable intervention option to improve the climate and pro-sociality environment at schools. © 2019en-USExperimental studyPhysical exerciseSchool healthStudent behaviourTraditional bullyinghttps://doi.org/10.1016/j.ijchp.2019.05.001