An IEP is a legal and binding document, I know because I am a teacher, so therefore if written, it must be followed or you can have a lawsuit on your hands. If I were you, I would contact the counselor prior to school starting, and make him/her aware of the problems you encountered with the previous year's teacher. I would then request a meeting between the counselor, the school psychologist and the teacher for the upcoming year teacher. Since you are his parent and this meeting would be your request they have to comply within 30 days upon your request. At this meeting, you would review the IEP and insure the modification and accommodations are in place for your son to be successful and allow you to voice your disappointment in the manner that things were handled last year as well as voice your the expectations you have of your son as well as the teachers. Perhaps, last year's teacher was new and inexperienced. I don't know if your son is on any medication, and I was not an advocate of medication for treating such, until I had a child. Then I became aware of just how much her inability to focus and calm was effecting her. It can be very frustrating for a child to have these issues that they are not capable of dealing with, so along with medication, I suggest counseling to help in behavior modification. I would consider the overall picture, your son must be feeling incredibly frustrated.
If you find this year, the school is unwilling to comply with the IEP, then I would call your state's coalition for children's rights. Believe we, they would gladly jump on this. I have seen it happen.
mother of three and master's degree in education