Just spoke with my wife about your situation. Depending on age, there are two options.
The first is to take your child to a doctor and get a letter from the doctor and apply for 休學. As long as you have a doctor’s recommendation this will be the easiest and quickest. Second option would be to discuss with the teacher at school, teacher will then speak with authorities and on and on. The second takes a lot of work and usually isn’t successful, depends on how much the teacher cares about the child and their improvement. But wife says usually way too much work and they won’t get involved.
Again PM me if you would like to speak in more details. She has helped quite a few of us big noses with issues such as this.