Knowledge bases require a considerable investment of time and money to construct. For many applications the dual use of a knowledge base in an expert system and in a teaching system would be cost effective. This research addresses the issue of whether a single knowledge base that can be used effectively in an expert system can form the basis of a functionally effective teaching system. To understand what is meant by a "functionally effective" teaching system a review of computer-aided instruction and intelligent computer-aided instruction systems has been carried out. From this, a list of twelve functional requirements were identified that should be met by the subject knowledge contained in a teaching system, and therefore by a dual-purpose knowledge base. A review of expert systems was also undertaken, and this resulted in the generation of the hypothesis that the deep knowledge approach to the construction of expert systems could be used for the construction of a dual-purpose knowledge base. A test system, DR MECHO, was constructed from the MECHO program, which solves problems in the domain of statics. This new system included: a deep knowledge base; a meta-interpreter, to provide explanations of the reasoning process of DR MECHO; and a set of actions, referred to as teaching actions, which could replace some of DR MECHO's usual problem solving operations with student input. The performance of DR MECHO as an expert system, and its ability to meet the functional teaching requirements, were evaluated. DR MECHO performed well as an expert system. It also met most of the teaching requirements. The main underlying reasons for the latter were: its performance as an expert system, the explicit structuring of the knowledge base, and the observance of the "no function in structure" principle (the latter two being characteristics of deep knowledge systems