If you havent already, I would recommend a meeting with his teachers. Is he being bullied? Is he distracted by others that he is sitting around?
My son was diagnosed with I-ADHD 10 years ago. It was so easy to manage early on but as they get older the work gets harder. He may feel its too much and mentally shuts down…unfortunately with everything. My son is now a junior in high school and what was a very predictable routine for him in years past has changed. He is now starting to drop the ball on homework assignments, fail to complete chores and becoming temperamental when trying to discuss these things with him. We may be back to medication in short order. I would love to tell you that it gets easier, it does for a while and then hormones kick it.
Have you tried a reward based system when he actually does his homework? When my son was that age, we did “pajama ice cream runs” when he had a good week and completed all his assignments.
Hang in there mom! You are on the right track.