Your link is about early childhood development and doesn't support the idea that any amount of time in Europe will change anything. A structured environment helps ADHD sufferers cope with symptoms, and quieter children (as the article claims French children are) are more likely to go undiagnosed, so a large part of the difference could be under-diagnosis. https://www.nimh.nih.gov/health/topics/attention-deficit-hyp... The article also claims that stimulants are the "preferred" treatment in America but it gives no source for this claim. On the contrary, Wikipedia cites papers showing that behavioral treatments are preferred for young patients and for mild cases. https://en.wikipedia.org/wiki/Attention_deficit_hyperactivit...
I think you should re-read the main article because you are completely missing the analogy here.
“Our ideas, our mindsets, and our beliefs feed back into the biology and change the biology in a way you can measure.”
+ are you missing the irony in my response to your ironic comment?
The point of the article I shared is that the classification of diseases in France does not include ADHD. Link that with the OP article and you'll see how the existence of a description of syndromes in the US can make these syndroms actually appear in patients.