There are many ways to use expert systems for teaching problem solving. The use of existing knowledge bases can help to reduce the cost of building new systems. We introduce an approach to use knowledge bases for classification problems as a domain model for intelligent tutoring systems. Most of the existing tutoring systems, that are really used in practice, are based on hypertext techniques with predefined links, that makes it hard to change or expand the presented knowledge or even to change the whole domain. Expert system techniques allow to formulate different knowledge bases for classification problems very comfortable. Here we focus on the didactic elements of case based tutoring systems generated from existing knowledge bases. The biggest advantage of these systems is the possibility to add new cases in a very short time without changing the systems itself or the knowledge base.