Hi & welcome! Just a few questions: How many hours of sleep is getting a night? And are you sure he's going to sleep when he goes to bed?
We had a similar issue with my oldest 'K', she has not been diagnosis'd (because bio-mom has interfered every time we've tried) but I strongly suspect ADHD & def depression. What I discovered was that when I thought she was asleep she was lying in her bed crying or just pondering everything that had happened in her day & she couldn't 'shut her brain off' to fall asleep so then she was super hard to wake up and get going in the AM. For the most part we have corrected this using melatonin to help her fall asleep quickly after getting in bed & she takes a daily vitamin plus B12 along with a glass of OJ every morning which gives her a good energy boost to wake up and get moving. Just a suggestion for some natural remedies that may help
You are also right that if he is feeling like the work is beneath him & he's not being challenged at all it could be why the teacher is seeing some restlessness and opposition. L is not in sped due to her IQ but we had to convince her teacher to give her extra work or tasks around the classroom to occupy her, otherwise she is all over the place being disruptive. I'm not a doctor of course but it sounds like there are some depression symptoms as well, which could also be due to not being challenged and feeling like he's stuck in sped doing work thats 'beneath' him. If he does have some situational depression this could also explain acting like he can't get enough sleep and being sluggish & unmotivated.
Smiling & Lucy are also right that a sleep study would help identify what is causing him not to get restful sleep.
Hope this helps
also you may want to create a signature (under settings at the top right corner of your screen) so you don't have to keep explaining your situation.
((HUGS)) & Welcome again!