There is increasing agreement among those who study classrooms that learning is likely to be most effective when students are actively involved in the co-construction of meaning through discussion of topics that are of significance to them. This paper reports the results of an extended collaborative action research project in which teachers attempted to create the conditions for such discussion by adopting an inquiry approach to the curriculum. A quantitative comparison between observations made early and late in the teachers’ involvement in the project showed a number of significant changes in the characteristics of teacher-whole class discourse, with a shift toward a more dialogic mode of interaction. Nevertheless, the frequency of stretches of “true discussion”, as defined by Nystrand et al. (2002), remained low. When the same observations were examined qualitatively, however, there was clear evidence of an increase over time in the teachers’ success in engaging students in co-constructing accounts and explanations. The paper concludes with a reconsideration of the purpose of “dialogue” in the classroom and of teachers’ goals and strategies in trying to achieve it.