Leadership is currently viewed as a guarantee for educational quality and reforms, as a crucial component for schools' capacity building and as a major contributor to the transformation of practices. Although an array of leadership studies report on the need for leadership by demonstrating what leaders must do or how leadership practices should be configured for schools to be successful, less attention has been drawn to how leadership is played out and how it becomes consequential in social practices. In this article, the authors analyse leadership as an interactive process, in a leadership team in a Norwegian school that aims to develop assessment practices. Cultural historical activity theory frames this analysis. The analytic concepts' perspective, position and interaction trajectory allow an investigation of leadership as an emergent property in the interactive process. Leadership emerges in complex chains of actions oriented by purposes constituted in the interplay of hierarchical and distributed dimensions of agency and authority. (Contains 3 notes.)