The role of discourse in education, specifically in the science classroom, is discussed. The discussion is based on the idea that talk in the classroom is not an end in itself but a means for inquiry, exploration, even activity, and expression of concepts. A framework for analysis of classroom discourse is outlined. In this approach, discourse is viewed as a tool-kit for achieving the goals of activities and their constituent tasks. The framework provides categories for analysis of the sequential organization of discourse and a theoretical basis for relating text to its context. The framework is then applied to specific classroom episodes, to explain how activities and their constituent tasks are operationalized through discourse. Focus is placed here on the role of the teacher, at both macro and micro levels, in engaging students appropriately with the curriculum, and more specifically on the use of responsive, follow-up discourse to accomplish this. Ways in which teachers can change their practice to match goals and action better are identified. (MSE)