The pointless message: We've banned dodge ball, the book Little Red Riding Hood ... so how can we possibly not ban guns, too?!
The reality: criminal misuse of weapons happens all the time, in schools as well, most particularly where banned. Hasn't stopped a thing.
The solution (at least partially): have good guys with weapons, sufficient to withstand/counter the bad guys with weapons; harden the facilities and procedures; segregate areas of the school from other areas; keep violent criminals who are caught out of our communities (either behind bars, or permanently).
The failure, and the real salient point of that politically-motivated ad: wishing criminals wouldn't ignore prohibitions won't solve a thing; nor will foisting more prohibitions on citizens.