This paper explores how students' talk in classrooms is influenced by a whole-school focus on lifting the quality, and the substantive nature, of classroom dialogue as an approach to improve student engagement, and to develop listening and speaking skills. Specifically, we show how designing and participating in whole-school professional learning projects emerged as a central condition for teacher and student development in the area of improving substantive classroom dialogue. The paper draws upon data from a larger, three-year empirical study in several Australian primary schools into the interconnections between professional learning, student learning, teaching and leading over time. In this paper, we focus particularly upon professional learning and its effects upon teaching and student learning, and illustrate how changing students' literacy practices require changing the practice architectures – that is, the broader conditions within which teacher and student learning occurs. Drawing on examples of teacher and student learning practices, we reveal the particular “sayings” (language), “doings” (activities), and “relatings” (relationships) which create and sustain the conditions under which students' dialogic practices can flourish. The research reveals that the practices of collaborative, critical reflexive dialogues on the part of teachers contributed significantly to the development of dialogic practices within literacy learning in classrooms.