I am an 8th grade math theacher and the parent of an ADD 7 year old so I see things from both sides.
As far as day to day from a teacher's perspective - Middle school is a whole other country. Some of the issues you are describing could be from the change of schools, from problems with not understanding the concept, from personality conflicts between the teacher and your son or from "middle school syndrome". Since it is across the board and not just one or two teachers, I would tend toward the latter.
As a teacher I see so called " normal " 8th grade students ( not ESE, not ADD or any other alphabet soup ) suddenly showing some of the same symptoms you are describing. The student who was one of the best and brightest,( smiling coming into class, answering all the questions, asking for help when confused, doing all the assignments, even helping other struggling classmates ) is now unmotivated, could care less about his grades, makes silly or even inapropriate comments in answer to a question, never does homework and doesn't even bring pencil and paper to class.
At our school, all students are given an agenda/planner notebook on the first day. One arrangement I have with a few parents of ADD / ESE students is that the student is responsible for copying the assignment from the board to their agenda. He/ she brings the agenda to me at the end of the period. If all the work was done in class, I cross it off and sign it. If not, then just a signature to show that the assignment was copied correctly and that the student kept up their end of the arrangement by coming to me daily. It takes me about 30 seconds and gives the parents the information they need, but still leaves the responsibility on the student to keep up with their work. For some of my students I also add a brief behavior comment from time to time, usually on Fridays. The parents know to check the agenda daily for homework, comments about missing work and behavior notes and initial that thet saw it. They also have a reward system set up that the student earns some sort of incentive for a full week of my signature, Mom's initials, all work turned in on time and a happy face for good behavior on Friday. It seems a little like Elementary school, but it works. Ask the teachers if they would be willing to try this. It is also a common accommodation for ESE students.
There is a definite difference between 8th grade and anything else. I have taught every grade from 5th to 8th, both "regular" sections and " intensive" or " remedial " classes with ADD / ADHD and ESE students included. We want them to be more independent ( getting ready for high school ) and so do they ( I'm 13, I'm not a child anymore). However, I have found that they need just as much structure and supervision as ever. You just have to make them part of the process.
What the school is required to do varies by state. Contact your son's school to speak to the ESE depatrment and the guidance counselor. In some states, ADD is not covered under ESE ( no IEP ) but is under something else. Here in Florida it is known as a 504 plan. The teachers are made aware that the student has a diagnosis and is taking medications. The school tries to schedule the ADD students into smaller classes and to make the students weaker subject in the morning when the medication has not worn off. The students are not given an IEP or any other ESE paperwork unless they also have a documented qualifying learning disability. It is up to the student, parent, teacher and guidance counselor to keep the student on track. Again, regulations vary by state, so you will have to do a bit of research on your state's policies.
Go ahead and check with your son's doctor about his medications ( pubery and hormones have strange effects on body chemistry ) and talk to your son's school about what can be done to help him. But ultimately, he is a middlle school boy ( who just happens to be ADHD ) and is still affected by all the typical middle school drama and adolescent attitude changes. He is just as intelligent an capable as ever, but unfortunately, the motivation has been overcome by hormones. The true battle ove every middle school teacher and parent is finding a way to make them care about more than video games and who's dating who. Good luck and God bless.