This article revisits Douglas Barnes's book-length exploration of the implications for teachers of a constructivist epistemology, notably in relation to the importance of small-group talk in classrooms. Empirically based consideration of small-group exploratory pupil-pupil talk enabled Barnes to reveal the learning strategies such a context elicits, and to argue for its educational significance. Barnes also considers how a curriculum can be seen as a form of communication. He identifies the importance of pupil engagement if learning is to be effective, and explores some of the patterns of communication which enhance such engagement. Barnes's attention to pupils' production of knowledge through exploratory talk retains its power to correct the view that teaching is essentially about the delivery of predetermined lesson-content.