This article reports a case study that investigated the ways in which heads of subject departments managed the development and application of new assessment strategies in one secondary school in Hong Kong. The data of the study were gathered through participant observation and interviews with 12 teachers who participated in an assessment for learning project in the school. The results show variation in the leadership approaches adopted by the department heads, highlighting the dichotomy between managerial accountability and professional empowerment as their perceived mandate, and techno-instrumentalism and autonomous explorations as their visions for school-based renewal initiatives. The findings of the study highlight the subcultures within subject departments resulting from the different leadership styles enacted by the subject leaders, and point to the need for further investigations into the mediating roles of culture of subject disciplines and contextual variables that shape the dynamics of educational management. (Contains 1 table.)