Tough teacher

A school teacher injured his back and had to wear a plaster cast around the upper part of his body. It fit under his shirt and was not noticeable at all. On the first day of the term, still with the cast under his shirt, he found himself assigned to the toughest students in school.
Walking confidently into the rowdy classroom, he opened the window as wide as possible and then busied himself with desk work. The classroom became a bit unruly and he admonished them. This happened several times. When he could do work at his desk, the strong breeze from the window made his tie flap annoyingly. He kept rearranging and rearranging the tie as the class raised its level of unruliness. Finally, becoming disgusted with the wayward tie, he stood up and took a big stapler off his desk and stapled the tie to his chest in several places.
Discipline was not a problem from that day forth.