Find me 10 successful entreprenuers and I bet I can show you 10 people who had a tough time sitting through unengaging lesson plans in school. Doesn't help with ballooning class sizes either.
As a child I would've been the perfect ADD candidate, but with plenty of stimulation in the form of work on my parent's farm, I winded up learning how to create outlets for my restless nature. There's nothing more boring or repetitive than driving a tractor around a very large field. My mind constantly wandered and in a few occasions led to damaged equipment because of it. Lesson learned and relearned. Another example would be pacing back and forth waiting to switch the milkers on the cows during the bi-daily 1-2 hr chores. Cleaning equipment, feeding, manure removal, stacking hay bales by hand. Repetitive, repetitive, repetitive, grueling.
School was fun by comparison. Even mundane lessons had their silver lining (at least it wasn't manual labor). And when I wasn't occupied with chores or school I found other stimulation; building a large purple martin bird house, flying model rockets, helping with mechanical repair, drawing, reading, shooting guns, exploring, painting ceramics, playing trumpet, and eventually, playing with our computer. The avenues of stimulation were not forced, but open. Most importantly: I could use the things I was learning in school to see how they had purpose, if not for my own satisfaction.
Why do these kids fidget and lack focus? In my non expert opinion it's because they lack both the perspective and a positive feedback loop to stimulate their own minds. It's not a disorder of the brain by any means, but a lack of purpose. Children reject the situations because they're contrived hoops with no meaning. The constant question in any child's mind is "HOW AM I GOING TO USE THIS?!" If they can't see the purpose of the lesson they haven't gained anything more than a useless set of facts.
Not being able to sit still is only one of multiple symptoms (from only one of the two categories - inattentive and hyperactive) used to diagnose people with one of several different sub-types of ADHD. (ADHD-HI, ADHD-PI, ADHD-C)
You need a certain minimum of symptoms for diagnosis.
Right now I have a strong pain in my left shoulder, I'm sure I am not alone in this right now of all the people in the world. I bet some of your successful entrepreneurs have had shoulder pain before. When it turns out I am not having a heart attack, and that all those entrepreneurs were not having a heart attack, would you think it correct to suggest that heart attacks aren't real? That is pretty much what you said above.
And beyond that, you need more then just a certain number of symptoms for a diagnosis of a disorder like this. There must be negative effects to your disorder in multiple spheres of your life. (home, education, romantic)
Suggested reading for anyone who doubts the existence of ADHD: http://dl.dropbox.com/u/9991388/2200_7-barktran.pdf
The test they give for an ADHD diagnosis is a joke too. Do have trouble focusing in class? Ah yeah, most of engineering teachers aren't giving daily TED talks... :)
I can't believe the parent got downvoted so badly. Did people think being dyslexic was an insult? It's not.