This paper presents interface guidelines from research at the University of Pittsburgh (Pennsylvania) School of Information Sciences in developing a collaborative, problem-based learning environment for the World Wide Web. The lessons learned are based on student use and evaluation of three interface prototypes over the course of 3 years and spanning several domains: (1) CALE I, an X-Windows application that includes functionality to support synchronous as well as asynchronous collaborative problem-based learning; (2) CALE II, a Web-based version of CALE I; and (3) CoMMIT, a frames-based Web application. Insights into appropriate windowing strategies, choice of menu structure and presentation, menus as a group coordination mechanism, and group annotation mechanisms are discussed. Extensions to the interface based on these findings are discussed, and directions for future research are given. Three figures illustrate the CALE I, CALE II, and CoMMIT interfaces. Contains 15 references. (AEF)