The social cognitive approach to moral development posits that moral self-schemas encourage character strengths and reduce adolescents’ aggression. However, limited research has examined the influence of positive personal characteristics on proactive behaviors and reactive aggression in bullying. This study examined direct and mediational relationships between forgiveness, gratitude, self-control, and both proactive and reactive aggression in bullying. The extent to which the structural relations of this model were invariant by gender and stage of adolescence were also evaluated. Participants in this study were 1000 Mexican students, 500 early adolescents (M age = 12.36, SD = 0.77 years) and 500 middle adolescents (M age = 16.64, SD = 0.89 years), between 12 and 17 years old. Structural equation and multi-group invariance analysis were performed. Results indicate that gratitude and forgiveness are positively related to self-control. Gratitude, forgiveness, and self-control are also negatively related to reactive and proactive aggression. Forgiveness and gratitude had an indirect relationship by decreasing both proactive and reactive aggression through their positive effects on self-control. Additionally, gender moderated the relationships between variables proposed in the model, whereas stage of adolescence did not. Overall findings suggest that moral self-schemas and strengths explained both types of aggression in bullying.