Thanks for everyone's input so far. I honestly believe its a cognitive issue with this particular student. His reasoning, judgment, and awareness skills are simply not there. For example, we flew four days ago and tower assigned him a routine taxi clearance to taxi to the runway via taxiway H. We get this clearance 97% of the time. He then proceeds to taxi to a taxiway D at midfield. When I asked him what it was he was doing, he said he was taxiing to taxiway H and points at D. Hopefully after spring break I will be able to schedule a flight for him with the chief instructor. After that, depending on how it goes, we will more than likely sit down with him and have a discussion.