Sounds like his treatment plan is not working well. Has this always been the case? That is, have you had success in the past in treating his AHDD/ODD? Do you have a medical professional who really understands ADHD and keeps up-to-date with research?
In the end, 11th grade is a point where he’ll need to at least have a desire to do well in school for any treatment to be effective. If that desire is not there, trying to force it will only makes things worse.
If it makes you feel any better, I quit high school in 10th grade. It wasn’t until I was 24 that I realized my options would expand with an education. Then, my ADHD hyper-focus kicked in, I got my GED and went to college. I really think if I had been forced to stay in school, I never would have wanted to go to college.