This paper focuses on mechanisms of “peer interactions” among native and non-native students. We present a theoretical framework based on Lazear (2001) education production model and on the “sub-cultural” sociological theory and we test the theoretical predictions exploiting a dataset of Italian junior high school. Results show that non-native school share has small and negative impacts on Language test scores of natives’ peers, while it does not significantly affect Math test scores. The negative effects to natives’ attainment are concentrated in schools characterized by low levels of non-natives’ isolation or where non-natives’ school share is above 10%.