We propose a novel model to simulate user knowledge consistency in tutoring dialogs, where no clear user goal can be defined. We also propose a new evaluation measure of knowledge consistency based on learning curves. We compare our new simulation model to real users as well as to a previously used simulation model. We show that the new model performs similarly to the real students and to the previous model when evaluated on high-level dialog features. The new model outperforms the previous model when measured on knowledge consistency.