Watch out for the quiet ones
My mom taught 9th grade general math for many years. As a math teacher, she had her choice of positions - and schools. She chose this particular school because she felt that she could make a difference there. Her justifiably high opinion of her teaching skills was part of that equation. The support of the no-nonsense administrators was the balance. She knew that any discipline problems would be dealt with promptly and effectively -- and with as much concern for the offender as possible.
She loved the school and the kids. They were nearly all from poverty-level homes and many of them lacked basic arithmetic skills. She chose to teach each one at his or her level - everything from first grade math facts to pre-algebra. She could control a class of 30-35 kids without ever raising her voice. Her students knew that she would not hesitate to send them to the office if they defied her - but that seldom happened.
One of her more trying students pushed the limits too far, using language completely unacceptable for the classroom.
When she ordered him to the office, he looked her in the eye and cheerfully announced, "You won't say that word out loud."
He paled as she lowered her voice and responded, "That's true, but I can write anything on paper."