Consensus exists that effective teaching includes capacity to adapt instruction to respond to student learning challenges as they arise. Adaptive teachers may keep pace with rapidly evolving youth literacies and students' increasing cultural and linguistic diversity. Teachers are challenged to critically examine pedagogy when some contexts expect compliance with scripts and testing regimens and impede innovation. Recent research is building cumulative knowledge on adaptive teaching in literacy--its forms, purposes, and values. For preservice teachers (PSTs) still developing curriculum and routines, developing adaptive expertise is particularly challenging. The present study examined how, if at all, a data- based model of teacher inquiry in one teacher education program fostered adaptive teaching in grades 7-12 English language arts placements in mostly high poverty, highly diverse schools. The study examined 96 inquiries collected over seven years, plus PST questionnaires, memos, and discussions. PSTs overall worked with classroom data in ways that discerned patterns in student work and used findings to change the means by which their objectives could be met, through adapting literacy routines, materials, strategies, and activities. Adaptations were complex, not always effective, often challenging as PSTs weighed alternatives, tried to align adaptations with data, and worked to develop data-based rationales for instructional adaptations. Inquiry processes that supported PSTs in adaptive teaching included close examination of data, discovery and reflection, alignment of adaptations with data, and critique of adaptations. A disposition of flexibility supported the work. Findings contribute to literatures on adaptive literacy teaching and preservice teacher inquiry in English language arts.