Factual Part
Closed campus lunch is when students are not allowed to leave school grounds to eat lunch without an explicit message from a parent. This is very common in most elementary and middle schools. However, most public high schools in the United States have open campus lunch. Many parents encourage closed campus lunch because they feel it is safer.
$0.02 Part
Recently they have been trying to make the campus at my highschool closed. The reason? People who live near the school are claiming that the students are participating in smoking, drugs, and prostitution. They've also blamed students for several thefts.
Now, we happen to have a nice big 45 minute lunch period. Now, as quick as some people can be, I just can't see a 45 minute prostitute. Not to mention some of the other reasons I'm about to mention...
Most of the seniors and juniors, along with a couple of sophomores, use cars to go get their lunch pretty far away from the neighborhood. I guess they just engage in some drive by theft, and keep their drugs in the car that's looked into every morning by school security guards. Yes, yes, I'm sure that's it.
Oh, and closed campus would make even more sense when we hav a lunch room that holds 200... and 1900 students. Oh yes, plenty of sense. And you know how public schools have that goldmine of money that lets them post guards at every exit to make sure kids don't go grab lunch...
Personally, I believe closed campus lunch is destructive, because it prevents kids from getting a good social experience. And it helps with math too, "Umm... how do you figure out the percent to tip?"