I think I'd give him a dose of real life. Not doing well verses doing well. I wouldn't appeal to his 'other' things that aren't going to lead to meaningful employment but rather that if he isn't able to function and live up to his potential, life WILL be harder.
My son is out of the box too as I call it and whether he likes it or not, this is his reality in life. He has a developmental delay. He needs to do things in order to handle the real life issues with his delay.
If your son is lacking motivation to do his best work, I'd try to figure out why. There are consequences to going untreated and I guess this is what I'd have a real heart to heart with him about.
lots of luck!
I should also say he was diagnosed with ADHD combined type and dysgraphia.
He has been evaluated by Kenney Krieger Institute in Baltimore twice now and he is scheduled to be reevaluated in July. I will definitely bring this up. My son is very laid back. Nothing really bothers him and he just goes with the flow. But even after repeatedly saying "write in your homework book even if you have to write 'none'" he does it for maybe two days and that is it. Then the zeros show up and then I get on him again. I can't go away to school with him and so I don't check up on him on a daily basis. I wouldn't be there to do that in college. I guess I have to see what the psychiatrist says. Thanks.
What do you observe he is good at, and what does he enjoy doing? Everybody enjoys something.
Has he had any counseling for ADHD? Does he understand what it is doing to him?
He has no idea what he wants to do.
He may not like the side effects. Ask him about that. How is his behavior outside of school, that is, outside of academic work? Maybe he does not want an academic career. Find out, if you can, what he wants out of life.