C.J.
It does sound like he is having issues processing his feelings emotions (they categorize it under social/emotional development). I have a 6 yo boy and he does not, nor do the other boys in his class, act out to this extent. I agree, you need outside, professional help on how he can learn to become emotionally competent and learn to express his feelings and emotions without yelling, hitting, or opting out of a situation.
In this case the teacher is not expecting too much from him. she is expecting what she expects (and is getting) from all her other students.
I don't know if it is possible to have early intervention (ECI) come out and assess him, but give it a try. http://www.nj.gov/health/fhs/eis/
Also, look into a child phychologist to help him re-learn how to process his emotions and his responses to being asked to do new things.
Good luck. this is such a challenging situation and I applaud you for not dumping it off as being the fault of the system or the teacher.