This paper describes GUIDON-WATCH, a graphic interface that uses multiple windows and a mouse to allow a student to browse a knowledge base and view reasoning processes during diagnostic problem solving. The GUIDON project at Stanford University is investigating how knowledge-based systems can provide the basis for teaching programs, and this paper specifically addresses GUIDON-WATCH as an interface to NEOMYCIN, a medical consultation system. Methods are presented for providing multiple views of hierarchical structures, overlaying results of a search process on top of static structures to make the strategy visible, and pictorially expressing evidence relations between findings and hypotheses. This work demonstrates the advantages of stating a diagnostic search procedure in a well-structured, rule-based language separate from domain knowledge. A number of issues in software design are also considered, including automatic management of a multiple-window display. (Author/THC)