["TESOL Quarterly, EarlyView. ", "\nAbstract\nDespite its potential benefits, empirical research on researcher–practitioner collaboration within collaborative teaching study groups (CTSGs) remains limited, particularly regarding how this collaboration is manifested and constructed. This study aims to fill this gap by documenting a 9‐year collaborative initiative that facilitated the implementation of task‐based language teaching (TBLT) at a Chinese primary school through a university–school partnership. Employing an ecological perspective, we aim to illuminate key features of an effective CTSG and how researchers and practitioners constructed a sustainable collaborative ecosystem that serves as a nexus between research and practice to support mutual development. Data were collected from multiple sources, including semi‐structured interviews, observations, field notes, teachers' reflective journals, and project artifacts. Our analysis revealed three collaborative features: co‐identified teaching study issues, co‐constructed collaborative contexts, and co‐created research‐practice products. We identified that the porous subsystems and the agentic beings navigating the intellectual, emotional, and economic boundaries of these subsystems are essential for establishing and sustaining an effective CTSG. The findings have significant implications for policymakers, researchers, and school leaders aiming to enhance the effectiveness of university–school partnerships.\n"]