The evolution and rapid expansion of online hate speech perpetration (OHSP) behaviors among adolescents toward different groups contrast with the lack of theory-based and empirically evaluated programs targeting this phenomenon. This study, developed by the Spanish Volunteering Platform, contributes to reversing this situation by investigating the impact of a service-learning program to prevent OHSP among students in secondary education. To do so, a cluster-randomized research design was adopted with a sample of secondary school students (n = 60) from two public schools. After the random assignment of each class group to either the intervention or control condition, the service-learning program previously designed was implemented for 3 months. Regression results in model 7 with all predictors and controls yield a significant effect on the variable experimental group = 0.803, p < .05, and gender = 0.987, p < .05, explaining 45.9% of the variance. The effect size for this intervention was 0.42. From a theoretical perspective, participants are moving in the right direction to reduce and/or prevent OHSP behaviors, which demonstrates the theoretical utility of the theory of planned behavior in hate speech research. Finally, several recommendations are made to improve the impact of future replications or adaptations of this program.