To be clear, I'm not in any way suggesting with this post that your child has been misdiagnosed. But there is no problem with underdiagnosing, ADHD is being overdiagnosed outragiously, and partly because it is what parents want to hear (that they are not bad parents).
ADHD is one of the most misunderstood conditions out there-
That is exactly right -not the way you mean though- and the biggest problem is that the name contains "hyperactive". Someone with ADHD isn't someone who has too much energy, the problem is in the nerveus system. The patient can't correctly process the signals coming from outside, which makes him confused and somewhat delirious, unable to focus. --If you want to experience a little what it's like, try not eating the whole day and then bingedrinking the whole night.-- The more tired he gets the less he is able to control his behaviour and do tasks. This is what ritalin helps for, it keeps the neurotransmitters going and keeps them focused. You could just as well give them speed or cocaine.
But you know what is worse than being undiagnosed for years not understanding why things are going wrong? It's being diagnosed as a sick problem child while there are other things going on. So if a kid can't learn at school, it might be because he has ADHD, or it might be because he doesn't sleep well at night because mommi and daddy fight all the time. Or because he doesn't get proper breakfast. And he may act weird because he has ADHD, or it may be because acting weird and "hyperactive" is the only way he gets attention from his parents (a conditioned behaviour), or because his parents are themselves not such good rolemodels, or just because he's a child. Real hyperactive children are exhausted all the time.