ABSTRACT This study aims to document how a research-practice partnership designed and carried out joint work between researchers and educators to support teacher instructional improvement. A district-wide research-based teacher professional program, grounded in research on student development of mathematical ideas, was adapted to the assets and needs of one elementary school. The primary source of data were field notes of meetings of the school instructional improvement team, involving researchers, the principal, and teacher leaders, and focused on the co-design of school-based settings for instructional support. A framework outlining key conditions of research-practice partnership success was used as an analytical tool to examine partnership design elements that support joint work towards both practice and research goals, partner practices, processes, and activities as they unfolded, and methodological tensions and opportunities. Findings highlight how centring relationships, shared goals, and relevance to practice supported researchers in gaining deep understanding of the local context and of the complexity involved in creating settings that facilitate instructional improvement within school systems. They also underscore the need for vulnerability and flexibility in researcher involvement. Future directions include supplementing data sources to examine co-design sessions discourse and through multiple perspectives and extending analyses to subsequent years of the partnership.