Background Research–practice partnerships (RPPs) are proliferating in education, generating increasing interest and posing many challenges. In this study, we shed light on the challenge of supporting practitioners> leadership and building capacity in an RPP. In the RPP literature, practitioner leadership is often highlighted as both a way to improve design development and enactment and as imperative for capacity building and sustainability. However, cultivating leadership also creates challenges which have not yet been adequately explored. Purpose We explore these challenges and related dilemmas in a large-scale Israeli RPP designed to cultivate teacher leadership and build district capacity. We investigate how local actors asserted their leadership, the resources they drew upon, and the dilemmas this posed for us as researchers in an RPP. We critically reflect on how we addressed these dilemmas, and the consequences and implications of our courses of action. Setting This study explores our partnership with two large Israeli districts, as part of a state-wide professional development reform supported by the Ministry of Education and a philanthropic foundation. The partnership aims to support teachers> collaborative, reflective inquiry on teaching and learning, in weekly in-school meetings facilitated by in-school leading teacher. The partnership began six years ago and currently includes 158 schools (458 leading teachers). Research Design We use linguistic ethnographic methods to analyze leadership assertion in three focal cases, representing three different leadership roles, at different levels of the system: (1) a leading teacher demonstrating creative non-compliance in the team meetings she facilitated, (2) a coach exercising her voice and authority in her professional development workshops, (3) and a district manager independently shaping structures. Data Collection Data were collected during the first three years of the RPP, including (participant) observations, audio-recordings, and field notes of in-school meetings, professional development workshops, interviews, and informal conversations. Findings and Conclusions The analysis shows that leadership assertion played an important role in constructing actors’ identities as competent leaders but posed dilemmas for us, such as how to acknowledge leaders> expertise while also maintaining program integrity. The case studies underscore the difficulties involved in managing a partnership in a large-scale educational intervention and the challenges to maintaining productive dialogue with different partners. The paper advances our understanding of the complexities involved in supporting leadership at different levels of the system, in day-to-day interaction, and at multiple micro and macro contexts in which it unfolds, in particular in a large-scale RPP.