Teacher professional development has been identified as essential to educational reform. Moreover, research suggests the power of inquiry communities in spurring teacher professional learning and shifts in classroom practice. However, not enough is known about what conditions within a community of inquiry might be necessary to inspire, support, sustain, and coordinate educators' investment in systems-level change. To fill this gap, this article reports findings from the last year of a longitudinal case study of a school district seeking to advance adolescent literacy in subject-area classrooms. We extended from prior findings to investigate whether and how educators' self-perceptions of efficacy and agency could be related to their engagement in a district-level, inquiry-based initiative. Participants were 43 teachers and school- and district-based leaders. Multiple forms of evidence (i.e., interviews, artifacts, field-notes) were collected and coordinated within a case study design. Findings suggested that the vast majority of participants experienced increases in efficacy that could be associated with their engagement in collaborative inquiry, which in turn had potential to fuel on-going change efforts. At the same time, leaders' careful attention to preserving teachers' agency appeared to support their sustained investment in continuous cycles of goal-directed practice improvement. Implications are discussed for structuring professional development within systemic improvement initiatives.