I don't think so. Check the video again. It's pushed under from the inside, spread apart as far as it can be and then locked into place. I believe most of the door jams are metal reinforced. Besides how is someone going to wield a sledge hammer and a weapon?

@BeeHappy Steel framed doors are better protected than wooden which with time the wood deteriorates or repeated hangings end up weakening the hinge seat. If you are saying that extending the horizontal sliding bar locks it into place against the door frame which I think you may be correct on when I revisualise the shape of the end plate will prevent it being pushed in. Looking at how much the door twists in from pushing from the outside identifies that the door is most likely made of ply or is of hollow construction. The probability is that a few shot gun blasts will see a hole big enough to walk through or blasts at the hinges will blow the door free allowing it to be pushed over.

Yeah, it's been a while since I have been in a school and I don't think they are all constructed the same. Some doors metal some wood? Idk, but regardless it is at least an attempt to slow down and hopefully stop an intruder. Failsafe, probably not, but it's something.

Not sure what good getting a hand through would do. I am guessing a broken wrist would be the usual consequence.

@Dick_Martin Yes that's a good point.