The first aim of this research is to introduce and to validate the new concept of School Normative Context, that revisits the concept of School Moral Atmosphere studied by Brugman and his colleagues through the SMAQ (1999) and validated also in the Italian context (Mancini & Fruggeri, 2005). The School Normative Context entails two new aspects: The first one concerns the interactive dimension of each specific school context and the second one concerns the perception of responsibility (internal vs. external) in the implementation of the norm. The second aim is to study the relation among adolescents' perception of School Normative Context, adolescents' orientation towards social rules and their aggressive behaviours against classmates at school. 268 students (mean age 17,01) attending three Italian high schools of three different educational levels (Lyceum, technical and professional) participated in this research. They filled a questionnaire composed of three parts: School Normative Context Questionnaire (SNC), Normative Orientation Scale (NOS) and Aggression Scale (Orpinas, Frankowski, 2001). School Normative Context has shown an acceptable degree of conceptual and predictive validity. The research has shown that the School Normative Context has an influence on the aggressive behaviours against classmates. Furthermore, it is a mediating factor between the adolescents' orientation towards social norms and their aggressive behaviours at school. (Contains 5 figures, 3 tables and 1 note.)