That's what they do now for earthquake drills, and it's what they did in the past as well. In the 1950s schools had nuclear attack drills. If a nuclear attack occured, you were supposed to "duck and cover" by getting down on the ground, putting your face against your knees and your hands over the back of your head. Doing that would protect you in a tornado or an earthquake, especially if you're also under a desk. But I don't think it would save your life if a nuclear bomb went off, especially if the nuclear bomb detonated right next to your school. And if it was a hydrogen bomb, you wouldn't just be killed, you'd be vaporized.
