This study was designed and conducted in an educational climate in which school and teacher accountability for student learning is increasingly connected to students' performances on standardized tests. The participants in this study, 5 middle school English language arts teachers, each rejected their district-sponsored data-driven instruction professional development models in favor of a more contextualized collaborative data-inquiry process: lesson study. Over a 2-year period, participating teachers engaged in 9 inquiry cycles focused on teaching and learning writing across participants' culturally, linguistically, and economically diverse middle school classrooms. This article highlights how participants' collaborative analysis of qualitative data broadened their knowledge for teaching and learning writing and promoted their development of a more responsive, rigorous, and integrated literacy pedagogy. Findings from this study suggest that teacher education and in-service professional development models that aim to support teachers in professional learning through data-inquiry must broaden the notion of what counts as data for data-driven instruction.