I hate to be discouraging. But I dealt with schoolphobia for 10 years until he finally dropped out. It is a real psychological problem. If you son starts having panic attacks, I recommend that you get a diagnosis immediately. Then you will have grounds to ask for an accomodation. These schools are awful with their inflexibility when dealing with children. Your son has a right to not be terrified in the classroom. All they have to do is switch his class. If the teacher requested it it would be done in a minute. But because a parent requests it, it is impossible. In 20 years of dealing with impossible schools I learned that the squeaky wheel does get the grease. If you complain enough, you will get what you want.
