I would look into getting him evaluated, just in case.

The nail biting and chewing on clothes, that could be a sensory thing as well. Some kids also do that when they are hungry. Some sites provide chews for students, you could let him use one in the car on the way to school. Does your child's school allow water bottles? If so, the sport kind with the pop-top is good for kids with oral/sensory issues.

A lot of this will depend on what the evaluation says, but it may help.

See this site for some chews http://www.therapyshoppe.com/therapy/oral-motor-fun-15/

Good luck with everything!

OP-

I would definitely look into getting your son evaluated, and check out ChildFind, your son should still qualify. There are a lot of other services as well. Just to help with any concerns, and if there is something going on to help get the help he needs.

Coming from a teacher--does your child's teacher use a picture schedule in the classroom? This can help kids recognize the routine and help ease anxiety. I also agree that I smaller classroom would be beneficial as he may be getting overwhelmed with all of the other kids and the noise. But I also understand wanted to try to stay with your current school and allow him time to adjust. With time, he may adjust to his current school just fine.

Some schools (i.e. Maddux School, TLC) offer smaller classrooms and cater to kids with IEPs or IFSPs (individual family service plans) if you decided that a change of school is needed.

Two thoughts. I have an acquaintance whose son's aggressive behavior was changed literally within the hour by trying Abilify. They had tried a handful of add Meds with no success, turns out he has a mood disorder. I never in a million years would have guessed he could have previously been described as an aggressive kid.

Secong thought: We tried Suzuki violin with our then 3.5 year old. What a nightmare. This was long before I understood that he has sensory processing issues and what exactly that entailed. At the end of our time with Suzuki, I rented a violin along with him, thinking I'd be a better helper/guider with practice if I understood it better. I tried the violin ONCE and was blown away by how incredibly unpleasant the noise and vibration was inside of my head. It was horrible, I hated it. I can only assume my young child hated it just as much as well, which is why the lessons and the practice were such a bear to get through. Definitely worth considering.

This is the OP again. Thank you for the advice. This is all so crazy. Tonight he was so sweet and good, but when he gets to school, it just makes him crazy.

He is doing Suzuki violin and he used to behave like I described in his private lessons. He would jump and the chairs, punch his violin and hide under tables. We used the Kazdin method for the private lessons and his behavior changed in two weeks. Now we are at the point where he misbehaves for about two minutes and then he is perfectly relaxed and compliant for the rest of the 15-minute lesson. After the lesson he is so happy that he was good and that I am praising him.

He seems to have this crazy reaction to any new "performance-like" situation.