My favorite example of this is my experience working at Chester High school (CHS). I went to work at CHS in April 2013 I was only out of high school myself for two years and still looked as though I belonged there. The first week or two as a security guard at CHS is difficult for everyone because the kids "test" you to see if you can take the heat, then as time goes they get a feel for who you are and what your morals are, when I say morals I mean if your truly there to work or if you have another purpose, we will talk more on that another time.
After my personal two weeks of heat I got to know some of the kids through small conversations in the hallway and mostly they were very pleasant! They would tell me good morning, ask me how my day has been, would talk to me about any issues they need help with etc.
Throughout the day I would get calls to remove student from a classroom, so naturally I would respond, and every time i would be shocked! Now I wouldn't be shocked by the student as much as I would be the Adult in the classroom. People always ask me why and here is why. If that kid can be polite to someone in a position of authority who looks young enough to be in high school then they certainly are able to be polite to someone who is more mature looking, which tells me that the adult in that classroom had approached that kid in a way that made them feel the need to act out. Now is that the case every time absolutely not but through my experience it happens more than it should.