Education researchers have established the value of dialogic, whole-class discussions across content areas. However, such discussions have been defined primarily in terms of questions that enable or constrain interactions among multiple students. Research remains to be done on whether and how the subject matter with which teacher and students interact during whole-class discussions can also enable or constrain the dialogic quality of their talk. In this article, I begin to explore the possibility that whole-class discussions may manifest in particular ways within a discipline. Based on sociolinguistic discourse analysis of three transcripts from a suburban, ninth-grade history classroom, I suggest that "imaginative-entry activities," which invite students to imagine themselves into hypothetical scenarios based on historical events, can promote or discourage whole-class discussions. Specifically, I demonstrate how the narratives co-told by a teacher and his students during these imaginative-entry activities discursively construct students' relationships to past events in ways that affect their participation in present classroom interactions. I call for further research into dialogic, whole-class discussions whose content and form differ from those in other disciplines.