UK national initiatives in education, such as the National Literacy and Numeracy Strategies, have been implemented to improve learning and raise standards. These initiatives place considerable significance on whole class interactive teaching, and political rhetoric makes great play of this pedagogic strategy. Teachers have been encouraged to use up to 15 minutes of whole class teaching in literacy and numeracy as a key focus for developing pupil learning. This paper reports on a two-and-a-half-year research study which investigated the nature and quality of these discourse episodes through analysing how teachers use talk in these whole class teaching episodes to develop and build on pupils' learning. The study explored how teachers use questions, how they capitalize on pupils' prior knowledge and how they help pupils become independent learners. A particular focus of the paper is to illustrate how teacher discourse can variously support or impede pupil learning, and how cognitive or conceptual connections in pupils' learning are often ignored.