Adolescents’ aggressive behavior is a growing social problem with important implications for psychosocial adjustment. The teaching of emotional skills has an important impact on reducing aggression in schools. However, little scientific evidence has shown the explanatory mechanism through which this training reduces aggression during adolescence. This article aims to provide evidence for the effectiveness of a 3‐year longitudinal intervention among adolescents in nine Spanish schools. A total of 476 adolescents participated. Results showed a reduction in physical and verbal aggression in Time 2 through the reduction in negative affect, anger, and hostile feelings, compared with an active control group. The training seems to be crucial for dealing with the emotional and cognitive components of aggression and, thus, their behavioral manifestations.