Your son sounds like an amazing little boy! I was just like him!! Although I am a woman, not a man, I was a know-it-all when I was little. Not like a bratty know-it-all, but I really wanted to KNOW IT ALL and I LOVED learning. BUT... it used to drive my mom crazy. I was so in my head that I didn't ever focus because my favorite pastime was thinking and learning and of course, I would get distracted from the here and now very easily.
Remembering back on my own experience, and I was thinking because he is so smart, perhaps give him the definition of focus. Here it is...
Focus: To zero in on a task and SEE it through to completion.
Let him know that includes SEEING it with his eyes until it's complete. Let him know that you think it's important he learns focus for all that he wants to do in his life. Connect focus with a dream he has for his future. Tell him learning to focus now will help him accomplish that dream. Then teach him his way: with definitions and ways to use his mental power. He might take it on to practice focus for fun once he 'knows' what it is...
Another thing is to define listening for him. He is so great at using his mind that you can let him know what listening is too. Tell him that listening is when you are NOT thinking (especially while someone else is talking). When I was little, I was so smart that I didn't ever have to listen to get good grades. Later in life, I realized I never really learned how to listen. I thought it was just focusing on your ears (I know, crazy, right?!). Your son is so smart, he is likely thinking while you are telling him all there is to do and handle and it's not that he forgets, he's just hearing you along with all his thoughts. With "Listen" and "Focus" as two things you practice AND they both take mind power, he might have fun with it.
Last but not least, I am a yoga teacher and we look at the body as a way to create balance as well. There are some poses that might open his heart up as well as ground him a little. Don't get me wrong, there is NOTHING WRONG with how he is... at the same time, these ideas might just work!
I ended up being a life coach and a yoga teacher because I was constantly looking for ways to balance, not squash, my spirit and perhaps some of the same things that helped me will help him. ;-)
with love and mind power!
K.