The ICTG research group is currently working on a Stroke Rehabilitation virtual reality system to improve prospective memory. In this system there is a need to give the user relevant feedback at the appropriate time. To accomplish this, we must model the user’s progress and understanding. Constraint-based modeling was used to create a user model and provide feedback. One of the main design decisions in implementing this was to decide when constraints should be evaluated. Other important design elements included determining what task the user is attempting. As well as writing the constraints, a constraint editor, scripting language and feedback generator were developed. A case study with a stroke survivor was conducted. This case study was used to further develop constraints. Two domain experts evaluated the validity and timeliness of the feedback and the validity of the fidelity of the user model.