Honestly...teachers can tell if a child has ADHD. If they have problems sitting and concentrating, or they have impulse problems...teachers also know the signs. I have lots of communication with my sons teachers to find out how he is doing on his medication....this way if it isn't working, I can take him back to his drs and find something else that will work better for him.
I do understand that some people think that if a parent would just be more strict with a child then they wouldn't act up like that...I hate to tell you that you are very misinformed!! Some children are straight up ADHD...they don't have a behavioral problem!!