Chat-based tools are often used for computer-supported net-based learning and knowledge construction. However, due to its media characteristics, chat-based communication frequently suffers from deficits due to incoherence of contributions, lack of coordination as well as related problems of awareness. These shortcomings of conventional chat-based communication pose severe problems for online knowledge construction and learning. We claim that these restrictions can be overcome and propose that extending the medium 'chat' with appropriate educational and conversational strategies embedded in the chat environment can actually improve the learning discourse and thus support collaborative knowledge construction. Relevant approaches and recent research will be reviewed. Conclusions for the design of chat-based CSCL environments will be discussed.