Marty - Our 16 year old cub (boy) is SOOOOO like that! My Gawd, if not for my own gray hair I'd think you had taken my son.
He's not diagnosed ADD, and certainly no vision problems (he reads the name of the advertising company off the bottom of the billboard before I can see the billboard.)
But, as a sophmore he's STILL having trouble getting his homework turned in. The thing is, he does his homework. He shows me that it is done. I watch him put it in his bookbag. He forgets to turn it in.
He gets side tracked on the way to clean his bathroom and ends up watching tv, in the kitchen fixing a snack, or even stops to put in a load of laundry. It's like the message is only in his brain for 10 seconds, then POOF!
Grounding hasn't worked for us. He's very ammicable, good hearted like your son, and not being defiant or bullheaded. He just gets sidetracked. Tell him he's grounded, can't be on the computer, can't do this or that, and he just goes with it. Doesn't bother him.
He was also reading and doing math and science before kindergarten with a constant need to learn more. Maybe that's part of the problem, but like we have told him, you can't be "brilliant" and "bored with school" if you're grades don't reflect that you "get it."
I have to go for now, but will check back later. If others have a "cure" I'd sure like to know what it is.