The "duck and cover" drills of the 1950s, when American schoolchildren crawled under their desks in preparation for a nuclear bomb, have given way to regular lockdown drills in many states to counter the threat of school shootings. The photographer Alec Soth recently visited the Belle Plaine public high school, an hour outside Minneapolis, to witness its routine. When the principal announced that a lockdown was in effect, classroom doors were quickly locked; students who were in the middle of gym class moved to locker rooms and secured the doors behind them. For several minutes, they sat on the floor, heads lowered. "It was pretty silent," Soth says. "They were fairly nonchalant about the whole routine." Julie Bosman

States that require lockdown or similar drills: 21

Lockdown drills required annually in Minnesota schools: 5

Fire drills: 5

Tornado drills: 1