Starting from the ecological framework, the present study aimed to examine the mediating effects of parental supervision and school climate on the relationship between exosystem variables (time spent with media and perceived neighbourhood dangerousness) and peer aggression problems (peer aggression and victimisation). The participants were 880 primary school students. The data were analysed with multiple regression. The results show that both mediators (parental supervision and school climate) have statistically significant partial mediating effects on peer aggression and victimisation. If students experienced more parental supervision, there was a decrease in the relationship between a) time spent with media and peer aggression, and b) perceived neighbourhood dangerousness and peer aggression and victimisation. Identical findings were obtained for positive school climate. Thus, positive school climate and parental supervision served as protective factors against the negative influence of dangerous neighbourhoods and excessive use of media on peer aggression problems.