I'm going to ask you to tell the teacher that she/he needs to deal with this and give your son absolute consequences at school and leave you out of it.
This teacher has to take her/his authority and use it. As long as the teacher is telling you on him and expecting you to manage his actions they are going to get the same results.
ETA
A 504 plan is perfect for your son.
An IEP is for people that have things like Mental Retardation, Autism, Severe Learning Disabilities, etc...think Special Ed. This plan is for kids that have disabilities in more than 2-3 daily living skills, they will often end up in the special ed classes in higher grades.
An IEP is NOT for kids who have seizures, diabetes, behavior problems, ADHD, and things that effect how they sit in the classroom and learn.
I still think you need to turn this over to the teacher and school to handle. Have them allow their own psychologist come in and observe him in class, let them do their own testing, if they recommend meds I'd suggest you start with Ritalin. It's completely out of the system in 4 hours.
It DOES NOT build up in the system, it does NOT show up in any tests after 4 hours. It goes through their system and speeds the brain function so it syncs up and works right. They have hardly any side effects from Ritalin. It's one of those drugs that have been around for a very very long time too so it's been tested and used many many many times.
Time released meds do build up, they do hang around and show up in blood work days after stopping it. They can tend to have many many more side effects that last all day and all night.
So for me it's Ritalin all the way. He's responding well and only takes it during the school week, 1 whole pill in the morning then a half at lunch time. He hardly ever takes another half after school but he does if there is some situation where he needs to sit down and pay concentrated attention.
We did give it to him on Sunday mornings before church. We gave it at 9:30 and you almost watch it wear off about noon or 12:15.