My dad said they would do air raid drills in elementary school (50's, 60's) due to the fear of a nuclear attack. They were taught to get under their desks.
Apparently getting under their desks was on the off-chance their school is far enough away to avoid being incinerated but still close enough for a pressure wave to blow out all the glass in the windows and turn it into projectiles.
That said, I suspect these drills were more for theatre, like most of the TSA is now - put up a big visible show that you're doing _something_.
Reasonable people can disagree.