Group activities as part of active-learning pedagogies are thought to be effective in promoting student learning in part because of the quality of discussion they engender in student teams. Not much is known, however, about which instructional factors are most important in achieving productive conversation or how these factors may differ among different collaborative pedagogies. We explored what provokes meaningful group discussions in a university physiology course taught using team-based learning (TBL). We were most interested in discussions that evoke explanations that go beyond statements of basic facts and into disciplinary reasoning. Using transcribed conversations of four randomly selected teams three times throughout the semester, we analyzed three distinct discursive phenomena--conceptual explanations, re-evaluations, and co-construction--that occurred in productive conversations. In this paper, we provide examples from student discussions showing the role of each of these elements in moving students toward conceptual understanding. These phenomena were more likely to occur in response to higher-order questions in Bloom's taxonomy. Preclass preparation and student accountability as part of TBL may be important factors in this finding. We share implications for practice based on our results.