Despite major theoretical progress in computer-supported collaborative learning (CSCL), relatively less attention has been paid to the problem of how research advances may impact schools and classrooms. Given the global changes and educational policies for twenty-first century education, issues of how research in CSCL can be integrated with classroom practice for innovation pose important challenges. This paper draws on experiences in Hong Kong and examines research-based CSCL classroom innovations in the context of scaling up and sustaining a knowledge-building model in Hong Kong classrooms. It begins with an examination of the rationale for CSCL research in classrooms and then considers a range of problems and constraints for school implementation. Classroom innovations involve complex and emergent changes occurring at different levels of the educational system. The experience of CSCL knowledge-building classroom innovations in Hong Kong schools is reported, including: the macro-context of educational policies and educational reform, the meso-context of a knowledge-building teacher network, and the micro-context of knowledge-building design in classrooms. Three interacting themes--context and systemic change, capacity and community building, and innovation as inquiry--are proposed for examining collaboration and knowledge creation for classroom innovation. (Contains 5 figures and 5 tables.)