I do not doubt that the results of the study mentioned by the OP are BS, and that there is an ulterior motive for the study. And I do believe that ADD and ADHD probably are overdiagnosed.
But if you have not lived with a child with ADHD, you totally and completely do not know what the hell you are talking about if you believe it is not real.
Has no one stopped and thought about the meds side of the story? AHDH meds are amphetamines and other STIMULANTS. Speed. Versions of the stuff people take to stay awake for hours on end.
What do you think would happen if you give speed to a normal kid? He would be bouncing off the walls. But if you give speed to a kid with ADD or ADHD, he acts as if it were barbiturates....calms down, chills out, etc, sometimes to the point of being zombie-like. This has been known for at least 50 years, when I was in high school studying drugs, one of the uses for amphetamines was already for hyperactivity. I thought that was pretty stupid-sounding. Until 25 years later.
I have a grandchild with ADD, and four with ADHD. All have taken meds, all have grown out of needing them. In all of them, the meds were the difference of pretty much not being able to function in school, and being on the honor roll every nine weeks. The oldest two grew up in my house. Both asked to be taken off meds when they felt they didn't need them any more. The one with ADD still shows many of the signs, but uses the hyperness to his advantage, he is in the US Army. The oldest with ADHD shows nearly no signs of it, he is a junior in HS.
It has nothing to do with parenting. I am not afraid to give the same corporal punishment I received as a child. It doesn't help. It is like they can't help but screw up. I was lucky though, I know of kids that tear doors off of hinges.