Computer mediated communication--including web pages, email and web-based bulletin boards--was used to support the development of a cooperative learning community among students in a web-based distance education unit for practicing science and mathematics educators. The students lived in several Australian states and a number of Pacific Rim countries. They reported increased satisfaction with their studies, decreased feelings of isolation, and better support for their learning processes. This article describes the iterative processes of research and design involved in developing and refining the unit, which was based in a social constructivist/constructionist conception of teaching and learning, between 1997 and 1999. Issues and implications for others planning to develop web-based teaching units, including the time and energy commitment involved, and the challenges of credibly assessing online participation, are also considered.