Negotiation is an essential component of collaboration: By means of knowledge negotiation, a group of learners determines what knowledge they have constructed together and accepted as a group. Within the European Union ITCOLE Project, we have adapted and extended the BSCW system that supports collaboration among professionals to a BSCL system to promote collaborative learning and knowledge building among young students in several European countries. We now propose enhancing BSCL with support for negotiation in small project groups within school courses. A review of theories of learning demonstrates the need for such support in a CSCL system. An appropriate conception of knowledge negotiation is discussed and a corresponding software support mechanism is proposed. The implementation of this support is described within a new version of BSCL slated for testing in 50 European schools next Fall.