Young children talking in mathematics: What is the point of 'that'?

As part of an intervention project to encourage exploratory talk with young children in mathematics, it was found that, although the children did not engage fully in reasoning, the intervention had supported some children in developing more cohesive discourse. The cohesion was evidenced through the children's use of deictic words, in particular the word 'that'. Examples of dialogue are contrasted to illustrate the changes in this use of deixis and are related to children's meaning-making in mathematics.