This case study research is informed by Vygotsky's view that talk is essential to organise our thoughts and extend our thinking and that, as Barnes suggested, the teacher needs to use the social situation effectively in the classroom to promote talk for learning. This article focuses on pedagogy and teachers' understandings of how talk works in the classroom, as I sought to illuminate teachers' intuitions and insights and their views of what they find challenging in organising classroom talk. Three case studies of "critical moments" in a lesson suggest that teacher knowledge about talk is located in concrete practices. The three teachers viewed a recorded lesson and chose a moment they defined as "critical" because the moment helped them to learn something about the way they use talk in the classroom. They then discussed this moment with me. These collaborative but critically evaluative processes are particularly useful for exploring and probing teachers' knowledge about talk for learning, an area of pedagogy that has proved so resistant to change over quite a long period. These three teachers suggest that such talk is becoming more marginal under the impact of performativity and the new cultural restorationist English curriculum.