Purpose: The purpose of this study is to understand how preservice teachers (PTs) learn about disciplinary literacy in English language arts (ELA). In mathematics and writing, research has found that teachers' participation in disciplinary work can support their understanding of domain-specific inquiry, problem-solving and argumentation. Design/methodology/approach: This exploratory, qualitative case study of an English methods course extends that work into ELA, asking how PTs' participation in collaborative literary reasoning (CLR) influences their understanding of ELA as a discipline and their instructional planning processes. Findings: Findings indicate that CLR supported PTs to define ELA as a collaborative discipline in which multiple interpretations of literature are valued; to name specific disciplinary literacy practices; to identify a focus and purpose for teachers' design and revision of lesson plans; and to inform their thinking about text selection and complexity. Originality/value: This work highlights the potential of collaborative literary reasoning to support PTs' learning about disciplinary literacy instruction.