Given that the subject department is recognised by subject specialist teachers as the central and immediate unit of organization in secondary schools it is surprising that so little attention has been paid by researchers to the leadership dynamics within science departments. The leadership dynamics within the science departments of two contrasting school contexts were explored dialectically in this study. The structure | agency and individual | collective dialectics guided our interpretation of data from lesson observations, interviews and questionnaire responses, especially as they related to teachers' preparation of units of work (i.e., planned curriculum). As well as recognising thin coherence in teachers' responses we identify contradictions in teachers' perceived and enacted leadership roles, and perceptions of influences on curriculum planning and teaming within the two science departments. Throughout the article we disrupt traditional individualistic leadership discourses and suggest possibilities for more widespread application of an individual | collective leadership dialectic in school science departments.