I used to be a student at a Islamic boarding school in Indonesia. I attended that school for 7th and half of 8th grade. There are many urban legends in that school that many people claim they've experienced. There's a ballerina phantom, a grandma that carries around a bucket in the bathroom, ghosts or demons that appear in pictures, the 3 girls that drowned in a well, and many more. This story, however, is based on my own experience.
When I attended boarding school, I used to get sick a lot. I actually had digestive problems, typhus, and I was diagnosed with Anorexia. People said that the supernatural tends to be attached to sick people, especially kids, because they are weaker. This would probably be why I used to experience so much. These "things" messed with me so much that my parents had to fly to Indonesia and take me back to America. I currently attend a boarding school in America too but fortunately I haven't experienced anything, at least not yet.
One night, I was extremely sick that it was hard for me to move around. I had 20 roommates and everyone left to go to the mosque because it was time to pray and I was left by myself. Teachers didn't believe when students were sick most of the time so one of my roommates turned the lights off so it would seem that no one was in the room. That's when it started getting weird.
First I smelled blood. It smelled fresh too. I ignored it thinking that maybe someone is on their period. My room was next to a bathroom and that bathroom tends to be littered with pads so this is why I thought this. I know, gross right? Then I heard scratching on the walls but I also ignored this. Then the door swung open. This startled me because the door is very big and heavy and there was no wind. It was actually very humid. My dumb self first instinct was to close the door so I crawled towards the door to close it. I was about 2 inches from the door when it slammed shut.
There are windows on both side of the door and when I looked up there was a woman staring at me through the window smiling at me and waving. Her teeth were yellow and rotting and I found that kind of gross. So instead of being scared, I was grossed out by this woman. I think the woman heard my thoughts because then she appeared inside the room and smashed a mirror that was on a dresser (only furniture in the room are the dressers and each student gets one so there's 20 dressers in my room) and left. The mirror breaking must've been loud because teachers ran up the stairs and barged into the room. When they saw me crouched on the floor they yelled at me and yanked me up. I got in big trouble that night because the teachers didn't believe me when I told them about the woman. But when I told my roommates they believed me because they always see her in the middle night sitting next to me and patting my back.
Maybe I am over thinking! But that's the feeling I got.
What gives me shivers is the mention of little girls being "checked" to verify whether they were on their periods - I hope the school had some non-invasive way of doing so!