Recent research emphasizes the context-specific nature of professional knowledge and expertise, implying that developing novel practices in authentic environments is a prerequisite for teachers' professional development. The aim of this study was to find out how teachers develop their practical knowledge and expertise through shared planning and to evaluate an innovative learning project carried out in an ICT-based environment. Two secondary school teachers of history participated in this study. The data were gathered using a multi-methodological approach (video recordings, interviews and questionnaires). The results are described in terms of the teachers' shared experiences and their increased awareness of their own scaffolding practices. Discussion is focused on the role of boundary crossing in teachers' negotiation of new meanings.