The present study is carried out with the aim of studying different situations of aggressive behaviour in the context of the relations among classmates. We addressed this issue with particular attention to two dimensions: the first one is related to the type of relations between mates (being accepted or rejected) and the second concerns aspects of evaluation, in terms of attribution of responsibility to the actors of aggressions and of the perceived degree of gravity of different aggressive actions. A questionnaire was distributed to a sample of 620 subjects, half males and half females, ageing between 11 and 14. The results are interpreted following three main topics. 1) Perceived gravity of aggressions, which is higher for girls than for boys, and which makes clear how serious are actions of theft while considers less important verbal aggression and gossip. 2) The attribution of responsibility to actors of aggressions, which gives emphasis to the discrepancy between general attributions (stereotyped) and the subjects' actual experience of aggressions. 3) Social competence, on the basis of which we identified four groups of subjects differing on the basis of the integration within the class-group and the evaluation of gravity attributed to the aggressive behaviours.