Analysis of the impact of professional learning and development (PLD) programmes for educators is complex. This article presents an analysis of a PLD initiative in which classroom teachers learned to use narrative assessment for students with "high" and "very high" learning needs. Using Cultural Historical Activity Theory (CHAT), the analysis showed how various tensions arose across the activity system of participants during the initiative. Tensions were associated with the roles of those involved, the narrative assessment approach, and the rules of the initiative. While the new narrative assessment approach resulted in benefits for the students and their parents, role conflict emerged in relation to established assessment approaches already used by the educators. It is argued that CHAT enables a more nuanced understanding of the complex ways in which teachers actually engage with official curriculum, pedagogy or assessment PLD initiatives, than do theories that position teachers as simply resistant to change. (Contains 2 figures.)