The purpose of this paper is to examine how Catholic district offices support school leaders’ instructional leadership practices at times of major reform. Design/methodology/approach: The paper employs the theory of practice architectures as a lens through which to examine local site-based responses to system-wide reforms in two Australian Catholic secondary schools and their district offices. Data collection for these parallel case studies included semi-structured interviews, focus groups, teaching observations, classroom walkthroughs and coaching conversations. Findings: Findings suggest that in the New South Wales case, arrangements of language and specialist discourses associated with a school improvement agenda were reinforced by district office imperatives. These imperatives made possible new kinds of know-how, ways of working and relating to district office, teachers and students when it came to instructional leading. In the Queensland case, the district office facilitated instructional leadership practices that actively sought and valued practitioners’ input and professional judgment. Research limitations/implications: The research focussed on two case studies of district offices supporting school leaders’ instructional leadership practices at times of major reform. The findings are not generalizable. Practical implications: Practically, the studies suggest that for excellent pedagogical practice to be embedded and sustained over time, district offices need to work with principals to foster communicative spaces that promote explicit dialogue between teachers and leaders’ interpretive categories. Social implications: The paper contends that responding to the diversity of secondary school sites requires district office practices that reject a one size fits all formulas. Instead, district offices must foster site-based education development. Originality/value: The paper adopts a practice theory approach to its study of district support for instructional leader’ practices. A practice approach rejects a one size fits all approach to educational change. Instead, it focusses on understanding how particular practices come to be in specific sites, and what kinds of conditions make their emergence possible. As such, it leads the authors to consider whether and how different practices such as district practices of educational reforming or principals’ instructional leading might be transformed, or conducted otherwise, under other conditions of possibility.