In movies how do filmmakers get permission to film in a high school?

I saw some movies that were filmed in real High Schools! Like "Kick- A S S" which was filmed at Sir Winston Churchill Secondary School (Hamilton) And "Superbad" which was filmed at El Segundo High School I am just wondering how did they film in a real high school? Was the school closed? And how does the school let them film their aren't they gonna ask if it's an "Educational movie" or a "Family film?"