The present study, based on data concerning 2328 immigrant children attending a representative sample of 561 schools, investigates the impact of various group, family and individual characteristics as well as proficiency in the national language on acceptance and friendship among classmates, while controlling for measurement errors by means of a structural equation modelling approach. As regards group characteristics, the results indicate that only immigrant density in the classroom has a positive impact on social inclusion, which seems to be limited to peer acceptance. As regards family and individual characteristics, low-SES and female immigrants appear to be doubly vulnerable in class, which specifically affects their friendships. One of our main findings is that proficiency in the national language predicts the social inclusion of immigrant children, while controlling for all the other variables considered. A moderation analysis reveals that this factor also applies to second-generation immigrants. In conclusion, we suggest that interventions aiming to facilitate the social inclusion of immigrant children should take into account the fact that proficiency in the national language appears to be much more important than group, family and individual characteristics, and that low-SES and female immigrants require particular attention, since they are doubly vulnerable.