I agree with the participant who said you son is being triggered by the environment. Medications help but are not magic wands.
In preschool my son refused to do a lot of activities in the class. I took him out. Then kindergarten came and he would do well with the main teacher but not the aids nor her reading teacher. Sometimes people need to know how to interact to create cooperation…maybe this school is not for him.
Small class, interactive activities with teacher who engage and are calm but firm worked for us.