Tutorial dialogues can be analyzed as an interaction in which a tutor "debugs" a student's knowledge representation by diagnosing and correcting conceptual misunderstandings. Some tentative steps toward a theory which describes tutorial interactions are outlined. The goal structure of a tutor, types of conceptual bugs that students have in their understanding of physical processes, and some of the representational viewpoints necessary to diagnose and correct these bugs are discussed. (Author/CMV)