So I suppose ADHD is a possibility, although the way he can spend hours focusing on his latest lego or erector set masterpiece makes me skeptical about that.
This can actually be a piece of ADHD as well... it's called "hyper focus."
ADHD kids/adults don't have trouble focusing on things they enjoy... they have trouble sticking to what they're supposed to be doing when it's something they don't feel like doing. The problem exists with the things they find boring or difficult.
(Except, scratch the "difficult" piece from a 2e kid - GT kids need challenge... my DS sometimes can only focus when he's challenged).
It's a...
metacognition issue. "I need to stick to this boring homework and finish it, because my teacher expects it to be done." Most kids would be "meh" about it, but an ADHD kid would be constantly pulled away by distractions, almost powerless to keep themselves on task. A 2e/ADHD kid, meanwhile, can sometimes compensate and get the work done.
This is a GREAT book that clearly illustrates the differences between typical ADHD, 2e ADHD, and non-2e GT.
http://www.amazon.ca/Different-Minds-Deirdre-Lovecky/dp/1853029645 I highly recommend it - it's a great read.
Anyway (I ramble, lol), what I originally wanted to say... a GT/ADHD kid could easily zone into an enjoyable project for an extended period of time. (This doesn't mean your son has ADHD, it just means that the ability to focus on what he enjoys doesn't rule it out).
