This paper examines the role of mediating organizations in helping schools engage in whole school change as part of a school district's reform agenda. Specifically, it examines the Learning Community Program in Los Angeles, a programme designed by an external school reform organization, to assist schools in planning and implementing LEARN (Los Angeles Educational Alliance for Restructuring Now). The programme's success is shaped by the district and school contexts in which it operates. As mediating agent, the Learning Community Program must balance the challenges facing the schools ‐‐ particularly their readiness to engage in reform ‐‐ with the demands of the district for scale, accountability and resources. As it does so, it faces the challenges of maintaining program flexibility, building sustainable changes, and preserving its organizational independence. These pressures generate three central dilemmas and threaten to undermine the success of the district's reform and the Learning Community Program ‐‐ scale versus sustainability, district mandates versus site autonomy, and organizational independence versus survival. It concludes that mediating agencies can be constrained by their dependence on policymakers for critical resources.