Intelligent Tutoring Systems (ITS) typically contain elements of instruction, assessment, feedback and guidance for the trainee. Most of the time, the ITS is controlling the dialogue with the learner, whereas the learner has a passive, reactive role. In this paper, we suggest a technique called "verbalization", which allows users to work independently in the domain of application, and still get useful feedback and support. The principle of verbalization is to generate a natural language expression reflecting the meaning of a user's input. We developed and tested this concept in VETS, a Verbalization Enhanced Tutoring System for PowerLoom, a knowledge representation language based on description logic. Our studies showed that verbalization improves the persistence of users in trying to accomplish their goals and consequently leads to higher success rates in solving given tasks.