This is a mass-media trope. It's as reality-based as a complaint that "It's horrifying that so many hackers are allowed to just walk into Pentagon's network with their visual-basic 3D IP viruses".

The reality is that ADHD can cause all kinds of problems with making decisions, planning, perception of time, staying focused on a chosen task, emotional regulation, and sleep. School just happens to be the first place where these difficulties become apparent, but this can be a struggle in all areas of life, and not everything can be helped with environmental accommodations.