There are dozens of these stories in a given year. It's shocking. It's disturbing. Add in the increasing number of female teachers (including one with HIV) molesting 13 year old boys and you have to think the world has gone mad.
I walked in on students having sex in a classroom twice in my 4 years, but the mental image burned into my mind was from my first day of student-teaching... walking into a new building, nervous and excited, and I in the stairway I pass a young man with a girl under each arm. He sees me walking up, looking at hime, happily and greedily makes out with one, and as I pass by with a slightly stern look (and probably some confusion in there as well), he non-chalantly turns and starts tonsil boxing with the girl under the other arm. A very quick lesson on what I was walking into.