I attended a girls' grammar school, and was very well-behaved and painfully shy. I even used to suffer agonies rather than put my hand up and ask to go to the toilet.
After a needlework class, when I was 13, the teacher picked up some paper from the floor. It was a very smutty story that someone had written. Unfortunately, she decided that the writing looked like mine!
Imagine my horror at being called before the (very intimidating) headmistress. I was a complete innocent, in every sense, and wasn't even sure what I was being accused of doing.
Luckily they must have realized from my demeanour that I wasn't the culprit, and I was allowed to go. Eventually the girl who HAD written the sexy story was detected, and expelled. She had a history of bad behaviour, and that was the last straw! Both the needlework teacher and the head were middle-aged, unmarried, and very strait-laced!