BackgroundTaking part in physical activity has a major positive influence on the development of adolescents. Research shows that physical activity has an impact on cognitive and behavioral functioning. Aggressiveness is a factor negatively correlated with school achievement and resiliency is a protective factor for coping with stressful situations. The purpose of this study is to analyze the mediation effect of resiliency as a dispositional protective factor in the relationship between aggressiveness and school achievement in the context of gender and levels of physical activity. MethodsThe research was carried out on N = 787 adolescents (Mage = 15.95; SD = .29) from the Pomeranian region in Poland. The participants were divided into three subgroups: 1) a non-active group, n = 130 (90 girls); 2) a Physical Education (PE) group, n = 490 (303 girls); and 3) an athlete group, n = 130 (65 girls). The following research tools were used in the study: a socio-demographic survey; a questionnaire about average grades at the end of the school year; the Adolescent Aggressiveness Questionnaire – Emotional Reactivity; and the Resiliency Assessment Scale for Children and Adolescents to evaluate resiliency levels. ResultsAnalyzing the average school grades, resiliency, as well as levels of aggressiveness and its components revealed statistically significant differences in terms of gender and physical activity. Furthermore, the effects of general aggressiveness level and all its components on average school grade, mediated by resiliency, proved insignificant for boys in all three research groups and for girls in the athlete group. However, the analysis showed a mediation effect of resiliency in relation to emotional irritability and average school grade in the group of non-active girls. The mediation analysis revealed significant mediation effects for emotional irritability, opposition, and verbal aggression, as well as for general aggressiveness levels in the group of PE girls. ConclusionsResiliency is a protective factor in the relation between aggressiveness and school achievement, especially in the female PE group. The mechanisms governing boys’ functioning seem different and require further research. Compulsory physical education classes may help build resources that facilitate learning.