Like good breeding yuppies (many years ago), my wife and I looked at a number of expert guides on child rearing. We saw that the advice of "experts" spanned 180 degrees, from "breast feed the child and let him sleep with you until he decides he's had enough" to "bottle feed and put him in his own room, letting him cry things out". We also saw that our yuppie friends tended to buy and follow the advice of the expert whose advice synced with their own intuition and needs. So, while the yuppies purchased a book, what they really were buying was peace of mind.
Before we lay the ADHD issue wholly at the door of big pharma, big food, big government or big education/experts, then, let's take a look at the parents. Having your child diagnosed with something takes away the blame and the guilt (though not the worry). Many parents who are used to performing at a 95%+ success rate at work cannot accept a child who does not perform at that same rate. I will invite condemnation by observing that, in particular, many high-performing women who have put their careers on hold or a side track to raise kids feel guilty when they don't score 95%+ as a parent based on their children's behavior and accomplishments.
Kids are kids. They develop with different personalities and at different rates. Most five-year-old boys simply cannot sit through a school day. (Diagnosis -- boy.) There is a range in which the child adjusts to the grown-up world and the grown-up world adjusts to the child. The French are at one end; most Americans tend toward the other. French children are generally well behaved, but French adults are not. If we start raising our kids the French way, when they grow up they will no doubt trash cafes to protest globalization. Children need and want structure to feel secure. There is a reasonable, though not always happy or tranquil, medium. I submit that in almost all cases, grandparents are better sources of advice than experts, and parents are more in need of sedation than kids. Chill out.