Don't worry if your under 11, that is the average age for having your period. I suggest if it does happen, don't call the nurse, instead use the restroom and use paper towels to prevent leakage. I have started puberty when I was nine or ten, and it doesn't come instantly. I have had my period and I suggest just to use paper towels (or if it already happened, then carry products if you worry too much.) There are signs, like period cramps (those are the signs I get when I'm having my period.) It's hard to tell when it's coming though.