An ADHD diagnosis often comes about because students' performance in school. If they struggle paying attention or there are behavior problems, it's a popular option to consider.
There's an underlying assumption that all of the teaching is the same. Or that the teaching is interesting and worth paying attention to. Or that it's even...well, good at all.
If all my teachers were like my 11th grade history teacher (who recited facts for 70 minutes every weekday with all the enthusiasm of a broken-down car), I would have been diagnosed with ADHD, too.
There are some amazing teachers out there. But there are a lot of boring ones, too.
Before we slap a diagnosis on our kids, we should check...just for the heck of it...that the teaching is good and reasonable to begin with.