There is an obvious growth in the use of distributed and online learning environments. There is some evidence to believe that collaborative learning environments can be effective, especially when using advanced technology to support learning in and about complex domains. There is also an extensive body of research literature in the areas of situated cognition and problem-based learning that provides a theoretical perspective for the design of such learning environments. What is lacking are intelligent support tools to make it possible for subject experts (teacher-designers) to be more intimately involved in the design and implementation of collaborative distance learning environments. This paper describes such design tools, explicitly drawing on a socially-situated view of problem-based learning in technology-mediated environments. It concludes with an illustration of the tools as applied by teachers to the domain of environmental education. (Contains 31 references.) (Author/AEF)