This paper reports on a five-year collaborative research programme, the aim of which was to create Computer-Supported Collaborative Learning Environments that favoured and supported the production of epistemic interactions for the co-construction of scientific notions. Three systems (C-CHENE, CONNECT and DAMOCLES) were developed and experimented with science problem-solving tasks within constraints of the French secondary school curriculum. A number of issues were explored in relation to our research goals, including: structuring the communication interface, statistically or automatically constituting dyads to favour conceptual confrontation, summarising points to be debated, and studying/defining the teacher's multiple roles in CSCL contexts. We discuss limitations of our research and bring out lessons that have been learned from this research programme, concerning notably: freedom and constraint in the communication interface, structuring collaborative problem-solving sequences, richness and negotiability of environments, interrelations between cognitive, epistemic and social dimensions of interaction, and evolution of new educational practices.