As a parent of elementary school child, I can tell you a lock-down can be terrifying. Last year on my son’s birthday I came home and noticed a police helicopter and a couple of news helicopter over my son’s school (a mile away). Another parent came driving by and told me the whole school was on lock-down, and all roads in are blocked by police and there were dozens of police, FBI, and SWAT vehicles on school property. I immediately drove as near as I could get to find out what was going on. He was right about the number of police cars. 24 of them they later said on the news.
Turned out a couple of 6th grade girls played a prank on another and told her to stay in the bathroom because a man was in the school with a gun. The prank quickly got out of hand when the girl ran out of the bathroom to the office screaming about the man with a gun.