This study explores secondary history, literature, and science teachers' learning in cross-disciplinary professional development (PD) designed to support inquiry in disciplinary literacy instruction. As part of a larger design-based research project, teachers participated in a three-year Teacher Network designed to build knowledge and pedagogical practices for engaging students in high-level thinking and disciplinary argumentation. Sociocultural principles of PD served as the base for Teacher Network activities. We examine how teacher learning occurred within this context. Analysis of final teacher reflections revealed that teachers appropriated, transformed, and conventionalized disciplinary literacy practices when positioned as empowered agents of change through collaborative work.