My 9-yr-old DS is having problems with his peers.
Does your school have a school psychologist? I think you need to find another adult that he will listen to and feel comfortable talking to about this and what things he can do to make it better for himself. Better by either being able to handle the teasing, shrugging it off or getting them to stop. Sometimes it is easier to hear and make changes when someone other than your mom or dad is giving you the advice.
It is possible that the kids are just as frustrated by his reactions to mild teasing and comments as he is. It makes it hard to know what you can and can not say to someone if they take everything personally. I worked with a guy who was very smart and a very hard worker but he took everything said to him or around him personally. If we had a meeting and the supervisor said something about needing to be careful when we updated our files on the computer (to do it timely) he was convinced it was about him and something he hadn't done. It didn't matter that it was actually because of something I had failed to do and even had mentioned to him when I was called on it. No it had to be something he had done that the supervisor didn't want to talk to him about so he brought it up in a meeting. Which was not how this particular supervisor was. He didn't like good natured ribbing yet also felt isolated when he wasn't included in it. I'd known him for a long time before we worked in the same office and I use to keep telling him that things were rarely all about anyone. That the supervisors in our office didn't have the time or inclination to go after a particular person. And if they did, it wouldn't be him because we had a couple of idiots in the office who were causing them more work.
I identify with exactly what you are dealing with!
It was good to hear from someone who can understand the frustration of having this GREAT kid that his peers just don't get to see.