If you want to see ADHD in action, I can introdue you to my son..
You can have a conversation with him, and you look at him and know he's not there. he may be talking to you about homework, or his math class, or what he did in school today, but while he's talking to you, he's on the 5 yard line, it's 4th and goal his team is losing by a field goal, and there's 3 seconds left on the clock.. and he steps up to the center to take the snap..
His mind operates on 8 cylinders ALL the time, he's never thinking about just one thing, but probably 4 or 5 things at the SAME time. He can watch a movie one time, and when you get a chance to watch it, he's reciting line by line entire scenes (more than just a little frustrating).
He's a good kid, that loves his mom and dad, and his brothers and sisters. He's a smart kid, that would have been held back if he had ever been diagnosed. He's somewhat socially inept, and can get you to the point of wanting to pull your hair out.. But he is who he is, and we love him, wouldn't want him any other way than him being him.