Repetition is used for a range of functions in conversation. In this study, we examined all the repetitions used in spontaneous conversations by 41 French adult-child dyads, with children aged 2 ; 3 and 3 ; 6, to test the hypotheses that adults repeat to establish that they have understood, and that children repeat to ratify what adults have said. Analysis of 978 exchanges containing repetitions showed that adults use them to check on intentions and to correct errors, while children use them to ratify what the adult said. With younger children, adults combine their repeats with new information. Children then re-repeat the form originally targeted by the adult. With older children, adults check on intentions but less frequently, and only occasionally check on forms. Older children also re-repeat in the third turn but, like adults, add further information. For both adults and children, repeats signal attention to the other's utterances, and place the information repeated in common ground.