This paper describes different design levels in the development of an intelligent tutoring system (ITS). Because the development of ITSs is difficult, time-consuming and costly, our ITS design proposal should make the process of ITS development less difficult and more efficient. Firstly, we present the knowledge types used in an ITS. Secondly, we describe our high level of modeling knowledge. Next, we define what we call an ITS-framework, and we show how such a framework can make the design and the development of an ITS more efficient. Indeed, the use of a framework gives us some interesting and important features: reusability, flexibility and extensibility. Lastly, we discuss our approach to the implementation of an ITS-framework and we introduce into that framework existing well-proven tools and technologies borrowed from different research results.