Have you talked to the principal and guidance counselor? Make copies of the notes, all of them, and give them to the principal. He or she should see them in aggregate.
A child this young shouldn't have been punished because of not knowing what to do about an overflowing toilet. Some children freeze with fear. It sounds like this teacher doesn't actually understand child development. This is a problem.
I'm not saying that your child doesn't have issues. He does. But his teacher is too punitive and quite franky, needs help figuring out how to help him. She's not willing to listen to you.
The school has a person, possibly the guidance counselor, who puts together behavioral modification plans for students like your son. Ask for one. If the principal drags his or her feet, let him/her know that you plan to write a letter to the school district requesting this service. Hopefully you won't have to go that far. With this plan, the teacher has to go by it.
On this site, you may have a teacher or others harp about never going over the teacher's head. I disagree with that. If you are appropriate and professional in manner, measure your words, and don't level personal accusations, the principal will understand and will help you AND the teacher. I've substitute taught for several years, and I've been a manager in business and the fact is that everybody has a boss and is responsible for a job, including teachers. You have every right to go up the chain of command when a teacher refuses to listen to your concerns about your child.
On a separate note, I'm not convinced that your son doesn't have ADHD. Kids with ADHD actually CAN focus (even hyper-focus) on things that interest them. I think you would be well served to work with a child psychologist to evaluate him. Your insurance should help with that. Talk to your ped about working with a play therapist as well. A play therapist could help with the perfectionistic tendencies that hamper his ability to move forward in the classroom. The play therapist can make recommendations to the school to be a part of his behavioral modification program. Outside evaluations have to be accepted by the school system to help your son.
If this teacher is not interested in helping your son, you would be within your rights to ask for your son to move to another room. Your pediatrician or the child psychologist can write a letter to the school explaining that your son needs the change. I would think that the teacher would want to help rather than have a letter like this show up. It reflects badly on her if you end up going to the school board over a behavioral modification program that is not followed in the classroom.
Lastly, I urge you to work closely with the guidance counselor to help your son. I understand what you are saying about not agreeing with how your son's teacher handles him. But when talking to the counselor, cite these examples and ask her to work with the teacher to help her help him. IF she is a counselor worth her salt, she will know what is and isn't appropriate. It's her job to deal with the teacher on stuff like this. With the behavioral modification program, the counselor will be part of the team anyway and the principal is suppose to monitor how the program is being implemented.
Best of luck to you all.