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i Intelligent tutoring systems (ITSs) are computer based tutoring systems that provide individualized tutoring to the students. Building an ITS is recognized to be expensive task in terms of cost and resources. Authoring tools provide a framework and an environment for building the ITSs that help to reduce the resources like skills, time and cost required to build an intelligent tutoring system. In this thesis we have implemented the Cognitive Tutor Authoring Tools (CTAT) and performed experiments to empirically determine the common programming errors that authors tend to make while building an ITS and study what is hard in authoring an ITS. The CTAT were used in a graduate class at Worcester Polytechnic Institute and also at the 4th Summer school organized at the Carnegie Mellon University. Based on the analysis of the experiments we suggest future work to reduce the debugging time and thereby reduce the time required to author an ITS. We also implemented the model tracing algorithm in JESS, evaluated its performance and compared to that of the mode