Its stereotyping. Its too often how they are educated, trained and the reinforcing culture they are exposed to on a daily basis. Even this day and time, its a very common opinion within the mental health profession and school environments.
A study done by Dr. Alessi, Professor of Psychology at Western Michigan University was very revealing in this regard.
"Please note that I am only reporting what I see, hear or read from the school district and difficult child, and correcting misinformation in hopes of helping facilitating development of appropriate goals for my daughter."
Ditto keeping the focus on difficult child.