If you have a somewhat checkered past yourself, you worry that they will repeat your mistakes or worse yet, get into more serious trouble than your own twisted teen brain had ever imagined.
One of the things that you dread the most is the call from the Principal or Dean of Students. They never call to say hello. If you ever get a personal call from them, it's usually because something egregious has occurred. Your mouth goes dry as they say Mrs. Soandso, I am calling about your son/daughter.
That is, unless they are calling you about the issue below, in which case you laugh hysterically, unable to catch your breath and eventually just hang up when they can't get a word in over your laughter. I haven't been popular with a principal since my son was in Jr High and I came this close to taking his ass out at Texas Hold 'Em at Casino Night. I let him win. He liked me. The High School Principal...not so much.