Wertsch's clarification of Vygotsky's claims about the role of social interaction in the development of children's thinking made an important contribution to educational research. Revisiting that clarification, I suggest that "talk" instead of "speech" best describes Vygotsky's concern with the functional dynamics of dialogue rather than the language system. Reviewing research on teacher-pupil interaction and collaborative activity amongst peers, I then consider what evidence has now emerged to support Vygotsky's claims. The article ends with a brief summary of the current state of our understanding about the role of spoken dialogue in learning and development.