Interactive whiteboards (IWBs) have rapidly become an integral feature of many classrooms across the UK and elsewhere, but debate continues regarding the pedagogical implications of their use. This article reports on an in-depth case-study from the wider T-MEDIA project (Teacher Mediation of Subject Learning with ICT: a Multimedia Approach). A key aim of the study was to draw upon sociocultural perspectives to develop a shared, grounded theoretical account of the processes through which teachers mediate subject learning incorporating use of the IWB and other resources. A series of six history lessons with a class of pupils aged 12-13 was videoed and analysed collaboratively by a university research team, the teacher, one of his colleagues and an academic subject specialist. We identify an emerging emphasis upon interdependent learning relationships in the classroom and illustrate how this particular teacher harnessed IWB technology to support a dialogic approach to knowledge construction in history. Strategies included communicating and developing complex ideas and modelling historical thinking processes through use of multiple digital resources; collaborative annotation of images and texts; spotlighting and reveal tools for focusing; and "drag and drop" for classification activities. Revisiting annotated slides served to draw on shared experience. (Contains 8 notes, 1 table, and 5 figures.)