The aim of this research is to compare the types and functions of repetitions in two different corpora, one constituted of verbal interactions between adults and multiply-handicapped adolescents, the other between adults and young children of the same mental age as the adolescents. Our overall aim is to observe whether the communicative (linguistic and pragmatic) behaviour of adults varies according to the interlocutor and, if it does vary, in what ways. The main results show that adults do not use repetition strategy with the same aims according to the interlocutor. When interacting with a child, repetitions form part of a strategy of linguistic "tutoring" which allow the child to take on board progressively more complex linguistic constructions; it also enriches exchanges from a pragmatic point of view. On the other hand, when adults communicate with multiply-handicapped adolescents, their main aim is the maintaining of dialogue.