When thinking about talk and discussion in primary science, the author often returns to the little gem of a book by Douglas Barnes--"From communication to curriculum" (1976). Barnes used observations of science lessons to make cogent points about the value of talk for both thinking and communication. A useful distinction that he introduced is between speech as reflection and speech as communication. In England, teachers have recently been reminded of the value of talk to help learning, rather than just to communicate what has been learned, by the training and dissemination programme for the Primary Strategy and the QCA/DfES materials Teaching through dialogue (QCA/DfES, 2004). The attention given to dialogue in these materials emphasises its relevance to learning in all areas of the curriculum. However, there are particular reasons for ensuring its place in relation to teaching and learning science. In this article, the author stresses the important role of dialogue in learning science at the primary level. (Contains 4 boxes.)