Part of the evaluation is an IQ test. He scored really high there - in some cases in the 98 percentile. But his ability to concentrate and stay on task is in the 25th percentile (or below), so the trick is to get the focus and attention up to a level where he can benefit from his intelligence.ADHD doesn't sound like the problem from what you've talked about. It sounds like depression. As for ADHD, that's an easy way for control, but stymieing potential. A lot of very smart people are told they have ADHD when in reality it's just being very smart and bored with the mediocrity they deal with daily.
The psychologist described it in terms of a high-performance car. He's a really good car (let's say for example a M5), with a really good engine, but he's running with one flat tire. Because it's such a good car, it can operate at the same level as a Tercel, even with the flat, but to get the full potential out of it, you want to fix that flat.
This is consistent with a lot of what I've read, and anecdotal evidence of a few of my buddies.
As for depression, I think you're thinking of someone else... wingnut perhaps?