[DonRotolo]

People like this are difficult to convince that they need to listen. I was once like that, and I had to learn the hard way that I really did not know it all. I am still driven to really and truly know it all, but I try very hard (not always with success) to not let it discourage others from contributing.

In my case I have a huge need to be seen as competent, and perhaps that's what this student needs as well. I am basing that on the different reactions to corrections from peers are mentors.

My advice is to have the mentors observe how this student interacts with peers and, assuming it's as you described, take her/him aside when the time is right and explain that, in fact, the other person was correct and s/he was wrong. This might take several days of observation. Then the mentor needs to explain that s/he'd best start listening to the more knowledgeable teammates, or risk jeopardizing the team's efforts.

All s/he needs is an understanding of the true meaning of team.

Ditto for the behavior at regionals - if incorrect or inaccurate information is provided, the entire team suffers.

Encourage, not discourage, the leadership tendencies, but temper it with the wisdom to know whey we have two ears and one mouth.

My 2 cents' worth.