When I was in high school there was a fence that ran around the entire outside area. It was about chest-high for most students, and covered in chicken wire, so all but the most unfit could climb it easily. A small number of students jumped over and back in every break, choosing to get lunch from a nearby cafe rather than the school cafeteria. Most people didn't, though.
I've been thinking a lot about the schooling system recently - thanks in no small part to Ivan's wonderful series of teaching posts - and what is especially interesting is how empty of real physical authority schools are. Teachers, now more than ever, are restricted with how they can manhandle children, and many parents are on the alert for physical and other abuse. Which is a good thing! But what it means is that teachers are given a strange task: to control and discipline students without any recourse to physical power. Disrespect a cop, and he can arrest or harass you (if not legally, then practically) but disrespect a teacher, and he can - what, yell at you? Send you to a more powerful teacher to yell at you? There's no credible threat of violence to back up the teacher's authority - and yet many teachers somehow manage to control their students.
The fence that surrounded my high school was easily climbable, but fences are never just fences. They're symbols of power, little signs that say: "you will be punished if you cross this boundary". If you fear the associated punishment, even a knee-high fence is impassable - if you don't, you can scale a fence that's twice your height. Even though the punishment was negligible in practice (a stern talking-to or an hour sitting in detention), almost everybody internalized the idea of fence-as-boundary very quickly.
It's not simply the fear of getting caught, either. When you are constantly surrounded by Authority, you develop (as I did) a little teacher in your head, or what the great philosopher Terry Pratchett calls a "policeman in your skull"*. Foucault wrote about the disciplinary powers of the 'panopticon', a prison where each prisoner is under constant observation. To be watched, without knowing exactly when or how, is to be always looking over your own shoulder. In the end, you police yourself; you fall victim to the great illusion that associates Authority with an all-powerful God. You become totally incapable of accurately assessing the actual power that authority figures - teachers, police, etc - hold over you. Even in situations where you know you can jump the fence and get away with it, you don't; or you do so with extreme agitation.
This is how you create and maintain authority over a huge group of people: you catch them young, you monitor them all the time, and you punish the extremely disobedient. It only takes minimal use of force to get people to police themselves - if most of them are already doing it. If you ate your lunch at the back of the oval, where more people jumped the fence, a strange thing happened. You saw people go over, and come back, without anything happening to them. You saw people break the rules and not get punished. You learned that you didn't have to police yourself, and that you could buy or eat your lunch wherever you liked. You broke a part - a very small part - of your conditioning.
The food at the cafeteria wasn't so bad. But food that you buy yourself, at a place you choose, tastes so much better.
* He put it much better than me, in Thud:
"Coppers stayed alive by trickery. That's how it worked. You had your
Watch Houses with the big blue lights outside, and you made certain there
were always burly watchmen visible in the big public places, and you swanked
around like you owned the place. But you didn't own it. It was all smoke and
mirrors. You magicked a little policeman into everyone's head. You relied on
people giving in, knowing the rules. But in truth a hundred well-armed
people could wipe out the Watch, if they knew what they were doing. Once
some madman finds out that a copper taken unawares dies just like anyone
else, the spell is broken."