We analyse social interactions during the first days of class in a secondary mathematics classroom (15 and 16-year-olds) with a high percentage of immigrant students. Our analyses show the co-existence of different models for both the interpretation and the use of classroom social norms and socio-mathematical norms. Valorising some behaviours over others appears as part of the discursive practices of mathematics classrooms. Local and immigrant students are not expected to behave in the same way, nor are they treated in the same way. The teacher and some students, who are familiar with the prevailing norms, cancel certain norms for a while in such a way that some immigrant students are excluded from fully participating in the mathematical discussion.