Students with intellectual disabilities are placed in regular education classrooms among other things in order to allow them to socialize with typically developing peers. However, the degree of social integration varies from one student to another. We hypothesized that the student’s social integration is facilitated when the teacher expresses a favourable opinion regarding the presence of the student in class, interacts with the student in a warm manner and facilitates her or his interactions with the other students in class. The teacher’s actions were assessed using a structured interview and the social integration of students with mental retardation was measured with a sociometric questionnaire completed by the group. Findings indicate that students were more socially integrated when their teacher acted to support their integration in class. We discuss the importance of considering teacher’s influence on the peer relations of students at risk of rejection or social isolation.