Three dimensions of dialogicity are emphasised in the literature: dialogic teacher talk, students' dialogic moves and organising for dialogic teaching. In this article, we examine these dimensions and the interplay between them in supporting dialogic argumentation in the context of whole-class discussions in mathematics and physics. Three seemingly different seventh-grade lessons were selected for further analysis from the database of a research project on dialogic argumentation. In this paper, we focus on whole-class discussions after a group assignment. The lessons were video recorded with multiple cameras and transcribed. We characterised dialogic features of teacher talk, more general teacher decisions and organising for dialogic teaching, as well as students' dialogic and justifying moves. In addition, we examined how these were connected. According to the results, the three dimensions of dialogicity played out differently in the lessons. Furthermore, the results give insights into the interplay of the three dialogicity dimensions and students' justifying moves in dialogic argumentation.