Yes, and in Florida they now think buckets of rocks in each classroom will work. /s
The bucket of rocks is for when the killer is in the room with you having passed whatever security your school may or may not have. Better to throw rocks at him than wait to be killed. My school sent us to a training put on by the local sheriff—it is called A.L.I.C.E. Alert, Locate, Inform, Counter, Evacuate. The idea being that the intruder alert is given, the intruder located, his location broadcast, anyone near takes counter measures, anyone distant evacuates. But, we were taught, if he gets in the room with you, rather than cower under desks, you attack him (since he’s going to kill you if you don’t). So, books, desks, chairs, hot coffee, (or rocks!) are used. Then rush him. Better to die fighting than hiding.