Software systems for educational purposes have been developed and used in many application areas. In this paper we will describe a development in the field of building science. ClAD is a teachware system directed to be used in the education of students of architecture as well as a tool that gives a survey to architects and engineers in the practice. In the first place it provides information about the use of computer science technologies in the building design process. Furthermore, information about the architectural design process itself is included. Based on an analysis of general requirements and specific demands of the application field we describe our solution concept. Very important conclusions are that the system has to integrate the use of all media which are usually used by architects by offering a flexible and well-designed user interface and allowing a high degree of interactive work. After covering the development process as a combination of top down and bottom up strategies we describe the overall structure of ClAD as a modular system which can be extended and updated easily. Finally, we give an overview about some parts of the system to demonstrate the implementation of the concepts mentioned above