I'm glad you wrote this. It's another story on why bullying doesn't "help a kid grow a back bone", which seems to be the typical attitude around here.
It's funny, my cousin has a similar story!
I was saying since he was a very young that he has a learning/cognitive delay. My family kept shutting me down saying, "He's so smart!". He is smart in the logical sense, but heaven's forbid you should get the blue flower on the cake. He had to have the blue anything. He also had very delayed motor skills, and still does but I think its more because of my aunt's laziness with reinforcing we MUST eat with a knife and fork.
Well a year ago, 4th grade, when he's grades were dropping, particularly in english. He couldn't read, write or spell so he was doing poorly in science and social studies too. Math was the only thing he was good at. They finally had a meeting with my Aunt and they brought up testing him for disabilities. Turns out he has an ocular tracking problem (he cannot track a bouncing ball with his eyes) and most likely a touch of ADD. There's a few other things too, can't remember.
On top of that he was being bullied horribly. He is awkward, was still into thomas the tank and pokemon (there are a LOT of asians in his school, so it might not be that odd), short and stocky/heavy set. He is like the perfect target. Just like your son, to the point where he had mentioned wanting to end his life.
What leaps and bounds this kid has made with vision correction, OT, and resource room. He is VERY techie so he is allowed to use a laptop or his tablet to write his papers in school. He's tests are all read to him and written for him, for now. He is REALLY thriving. The bully situation is getting better because he has started band and is flourishing so much they gave him a solo. My aunt said the teacher said they never have given a first year student a solo ever. He is so motivated to learn music he teaches himself, then teaches his class mates, who now like him because he is good at something.
It's so important to stand up for your kids! It wasn't until my Aunt "wanted answers" did anyone do anything. Testing and extra services cost more money, and a lot of schools are reluctant to put it out. Sad, but true.