“It’s like the front lines of a war,” said Emily Rubinstein, a sophomore at a New York high school. “Being seated in front of the classroom could be what makes you live and what makes you die.”

Emily has given a great deal of thought to her safety as she moves through her school day. She considers her English classroom the safest. It has just one door, and it’s down a hallway that makes it hard to find. Also, the room has an unusual cutout corner, with no desks in it. That would be one of the best places to hide if someone started shooting at Stuyvesant High School, in Lower Manhattan.

Math class is where she is most exposed. She sits in the second desk of the second row, in a direct diagonal path from the door. On lockdown drills, she has learned that the safest place to be is pressed up against the wall where the door is, so that if a shooter looks into the room, it will appear empty. But in math, she has calculated that her chances of reaching that position are low.