One possible approach to reducing the cost of developing an intelligent tutoring system (ITS) is to reuse the components of an existing ITS. We used this approach to develop an Andes probability tutoring system by modifying the declarative knowledge of the Andes physics tutoring system. We claim that if we cluster various educational domains into groups based on their problem-solving methods [2], then it will be more efficient to port an existing ITS to a new domain in the same cluster than to build a new ITS from scratch.