I feel your pain on so many levels! As a former teacher, I saw so many kids struggle in my classes and others. We had team meetings, with and without the student, and all those parent conferences. We tried to find an acceptable path for each child, whether that meant making accommodations, giving un-timed exams or giving extensions. We had progress meetings. We figured out new ways to post homework and issue reminders.
As a teacher and as a parent, I also looked at expectations (mine, my husband's, my son's, and those of my students and their families). We put kids into this system of learning in a certain way (or sometimes alternative ways) to master specific subjects and to be able to take standardized tests in those areas, in order to go to college. In many circles, vocational schools are viewed only as places for those kids who can't "make it" in academic settings. So many of us, and many of our kids, see voke schools as "settling" and a place of last resort.
The other thing is, kids just don't have the long-term vision yet. We can ask them what they want to do and what their plans are, but they just don't know. They say "college" or "get a job" or "military" because that's what their friends are talking about. They really have no idea, and because their brains aren't fully developed until around age 25 (particularly the part of the brain that can predict and evaluate consequences), their imaginings really aren't very accurate or realistic. So getting them to do X today to prevent (or allow) Y on the weekend or Z next summer just isn't workable. Even if they agree logically, the teen brain (and especially the teen ADD brain) can't follow through. This leads to unparalleled rebellion and frustration.
It sounds also like you have gone through hell - you've tried things every single way (supervise, don't supervise; nag, don't nag; restrict, don't restrict). So you're finding the same frustrations because you've tried everything and nothing works. It's so hard to know whether trying so many things is a good idea, or whether it muddies the waters because the kid gets confused about what his "rules" are. This is harder in the ADD brain because there's already so much going on in there, all these discussions and rules and consequences just create more chaos in a brain yearning for calm.
I have many friends who have gone through this too. One particular friend, a teacher, was really stuck where you are - her son had ADD and it was coming up to the time to get a driver's license. She was scared to death to have him behind the wheel where his lack of focus could have life-threatening consequences, both for him and for others on the road. That was the line in the sand for her. She had not given him medication because she had seen so many kids not do well on it in her years of teaching. She saw side effects and no effects. She saw kids on a variety of medication types and dosages, and she observed how difficult it was to find the right one (type, dosage, schedule).
She had a lot of connections with people who felt that the medication changed their personalities and they really didn't like who they were, either on the meds or off. She also had tried a lot of supplements but learned how poorly most of them are absorbed (same thing with meds) - despite their cost, most pills are only absorbed around 25%.
When you say you have been through all of these things, I wonder if your son has had the same issues. It's so hard to know what the right one is, what the right amount is. Even if you get it stabilized, the child then grows and gains weight, and that throws everything off. Then come the teen years with hormones, and it's a whole new ball game.
I now work with a lot of people who've gone through this as well, and I'm happy to say that we have found something that works. My son went to college, my friend's son got a driver's license and went to college, and another friend of ours got his personality back after going off his meds and finding something that did work for him. Another woman I know, who has years of experience in the classroom, has 2 sons who've had to find their own path with "academic" vs. "vocational" paths, but who've also found new focus.
For all of us, it has been a combination of things. I can tell you from my professional work in epigenetics and cellular nutrition that all supplements are not the same. There is also new and exciting work being done, with the most well-researched and studied nutrients that actually work on the epigenetic level (that is, the material surrounding the genome which tells each cell's genes what their job is). When there is damage to the epigenome (through environmental causes, lifestyle choices, disease, and other factors), the cells (including but not limited to brain cells) just don't work properly. We've seen tremendous changes in kids and adults with ADD, ADHD, Asperger's, sensory processing issues, OCD, PDD and many other problems in as little as 3 weeks, with continued improvement over the next few months. I usually advise people to have a 90-day framework in their minds, but to hope for evident changes much sooner than that.
So there are many paths open to you, and to your son. All of them have possibilities and challenges. I send you strength and support, as a parent, educator and consultant. I know it's especially hard because you are tutor and your work benefits so many other kids - yet you see your own son struggling. You worry about his success, you worry about his emotional state, and you worry about your relationship with him. I can tell you that my son found his solution, got organized and focused, went to a good college, and now has a successful career (to the extent that someone less than 2 years out of school has success!). But I foresee great things for him. Mostly I am thrilled that he is happy with himself.