Ok I have a confession to make.

A long long time ago, back in my early 20’s, my school-teacher girlfriend and I had sex in a book closet at her school.

BUT!  It was on a Saturday, the door was shut and locked, and there were definitely no kids around, maybe some Janitor on the opposite side of the school, and it was the 80’s.  (If that helps)
 

From YahooNews: 

Teachers quit after students witness sex

TAMPA, Fla. - Two middle school teachers resigned after students saw them having sex in a classroom, the school district said.

Frances J. Sepulveda, 30, and Bryant J. Wilburn, 29, said they had sex in the classroom during school hours on “one or two occasions,” according to an investigation by the Hillsborough County school district.

They resigned last month after two students at Coleman Middle School reported they saw the teachers having sex. The classroom door was locked and a window was covered with paper, but a boy and a girl told school officials they could see inside.

(more here)