Skin in the Game
In reply to Bastian (msg # 1792):
You've really bent over backwards, IMHO, to hold a private session with him to go over what to roll when. When doing that, did you get the sense that he was trying to learn, or just tolerating you? If the former, then it sounds as if he does want to play, but has a learning disability of some sort.
You might try a different way to identify dice, which could help. That is, rather than telling him "use a d20 to attack," tell him "use the red die to attack," etc. You'll have to put together a set of dice for him that stays consistent, but that is pretty easy. If he has trouble recognizing between types of dice, then it would explain him succeeding during your private tutorial and then failing later -- he was recognizing dice according to some criteria that you didn't realize, and they've changed in a way that seems irrelevant to you but confuses him.