Recent years hve seen the increasing use of expert systems and expert system shells in industry and commerce. However, there has been little use of the technology in schools and colleges, partly due to dissatisfaction with the available software. This thesis describes the design, implementation and evaluation of an expert system shell for use in education. An initial evaluation was carried out to establish some criteria for the design of the new shell. This comprised an evaluation of expert system shells by experienced teachers; an evaluation of several expert system shells by the author; and a case-study visit to a school Computer Studies department. The teachers were also asked for their views on the possible uses of shells in the classroom. An expert system shell was designed and implemented as a result of this evalation. This has an environment for building knowledge bases; an environment for consulting knowledge bases; a knowledge representation language allowing separation of domain and problem solving knowledge; and three supplementarty tools. The most important of these is an explanation tool, which allows exploration of the domain knowledge in a knowledge base. In response to posed questions, the tool can produce domain-based explanations using a domain-independent generation technique, and each explanation can be explored further through relevant follow-up questions. This tool provides a means whereby users can learn about the domain of the knowledge base being explored. An evaluation of this shell by teachers with previous experience of expert system shells suggests that it has the potential for use throughout the school curriculum as an educational medium.