The academic challenges of ethnocultural diversity in Montreal, often fuelled by immigration, have usually been been analysed in terms of academic success. However, negative social interactions or lack of positive interactions experienced by students constitute a risk for their psychosocial development. For immigrant students, that risk becomes more and more complex by being grafted with other challenges : a loss of landmarks, a new social network, intensive decoding of codes of sociability, etc. Based on an ethnographic approach combining observation meetings and interviews with various protagonists (children, parents, teachers), this article describes the dynamics of social interaction in pluri-ethnic classes and presents two distinct relational profiles (rejected and popular). The benefits of a finely tuned understanding of relational dynamics are analysed: for class management in a pluri-ethnic context, for a better understanding of the school-related stress experienced by immigrant students and as well as for an effective support by the teacher and the parents of students' socialization process at school.