I have to back up Lynn here; but I'm going to go further. It sounds to me like you're taking charge in the absence of a leader, and the junior student is resisting. This is a classic example of breakdown due to lack of leadership, not necessarily personality. You said "If there were a clear leader/Sensei, or authority structure, there would be an obvious solution". If there were a clear leader, the problem likely wouldn't have occurred in the first place.
My advice would be this: set up a meeting with your 'peers' - the other 2 senior students. Decide amongst yourselves who is in charge - it should be the most senior, but if they can't or won't, someone must. You could, I suppose, ask the black-belt that comes in weekly to help, but he/she isn't there all the time, he doesn't know the personalities involved as well as you yourselves do.
This sounds like a side problem, that the main problem is one student's attitude. In fact, it is not - the student's attitude is an effect, not a cause. He feels in his own mind that you, who have taken leadership upon yourself, are not suitable as a leader/instructor and therefore refuses to accept your leadership/instruction. With the leadership organized, he wouldn't have the option, he would be required to accept, or find another dojo. If that sounds harsh, too bad - no school worth the money paid lets the student elect his leader/teacher. That's the real issue here.
Hope this helps.
Last edited by DaveO : 08-06-2002 at 04:08 PM.