Periods are pretty hard to predict at first. Some people experience PMS (premenstrual syndrome) symptoms in the days leading up to a period so they have a little warning. These symptoms can include abdominal cramping, bloating, sore breasts, mood swings and acne. When your periods do start they may be irregular for a year or so - this is normal. Eventually they usually settle into a predictable rhythm of every 28 days or so. Keep some pads or tampons on you in your school bag or purse in case they start unexpectedly.