[cabmandone]

I went over your OP again and have to think there's some external pressure that's being missed. Getting good grades, Has friends, Participates in activities.
What does he do for stress relief? Is there some activity he enjoys that maybe you could take part in with him? I found as my son was growing up that taking part in activities he enjoyed gave me time to be with him and sometimes ask "how's everything going?". If you're not doing it already, make yourself as available to him as you can. You'll find he'll open up to you and when he does, be prepared to listen and don't "poo poo" his concerns and try not to marginalize his worries. Sometimes really listening and then trying to draw from your own life experiences really helps.

Good luck and I hope you figure out what the underlying cause of his anxiety is. Like I said, I've been there and I know it's no fun.

Edit: Make sure the problem your son is having doesn't become a problem between you and your wife. Sit down with her and work on a plan of action. Make sure you're listening to her concerns and do your best to articulate your concerns with homeschooling. But it's important that the two of you come to an agreement on the best path forward for your son. Again... good luck.