Drawing on research from online, knowledge-building, and discussion-based learning, this design-based experiment captures the instructional moves theorized to develop student capacity in progressive, literary discourse. The experiment employed Knowledge Forum and its unique capacity to scaffold student learning of progressive discourse that results in an explanatory model, theory, or literary interpretation. Analysis of student discussion posts within and between two iterative phases suggest that explicit instruction in progressive discourse, combined with regular classroom debriefings of online discussion, contributed to student mastery. Additionally, the use of sentence starters aligned with each Knowledge Forum scaffold for progressive discourse provided positive outcomes. Implications for using online, progressive, literary discourse scaffolds to inculcate disciplinary thinking and discussion appropriate to the secondary English/Language Arts class are discussed.