Background/Context: Although calls for rich discussion and argumentation about disciplinary texts and content are frequent, research indicates that in classrooms such discussions are rare. When discussions do happen, few students tend to participate. Purpose/Focus of Study: We look to exemplar teachers’ classrooms where a range of ethnically, racially, linguistically, and academically diverse students participated substantively in discussions throughout social studies inquiries to understand what those teachers do to support broad and substantive student participation in discussion, knowing that discussion promotes student learning. Research Design: Using video recordings of class sessions, we conducted discourse analysis and used case study methods to examine classroom discourse over 20 days of inquiry across an academic year within the context of a larger, design-based research project. Findings: We identify how two teachers build toward and facilitate three types of disciplinary, whole-class, text-based discussions: Sensemaking, Argumentative, and Culminating Argumentative. We analyze the instructional work involved in preparing students for discussions, in situating discussions within a larger context of inquiry, and in facilitating discussions in the moment, focusing on the intellectual work being done when students take extended turns of talk that build on what has been said before. Conclusions/Recommendations: This work contributes a broader understanding of how students’ full participation in disciplinary discussion and argumentation can be supported in the context of inquiry. We draw implications for enabling all students to participate in inquiry, with particular attention to students learning English or needing support for reading complex sources.