This article analyses the sort of classroom talk that leads to effective learning, and some of the forces which operate against such practices. It starts with an analysis of the classroom context and the dominant patterns of interaction. These cause processes of learning to be hidden. It then develops by an analysis of effective learning, comprising four headings: active, collaborative, learner-driven and learning-focused. Under each heading important forms of classroom talk are analysed, and principles are offered for developing improved practice.