That's a rare circumstance that is made to seem more common by very wide media coverage. And even in that sort of situation, it seems doubtful that it actually helps anybody either. Some parents will show up and get in the way of emergence responders. Most kids who call their parents will end up surviving anyway, and the phonecalls end up increasing the number of people who get PTSD from the whole thing. If a modest sized school of 500 kids has an above average shooting which kills 20, then you have 480+ parents getting a premature ""last call""; all would have been better off hearing about the incident after they already knew their kid was safe.
These kinds of calculations aren't useful to a typical US parent who, after the Uvalde disaster, has absolutely no reason to trust law enforcement to handle such a situation competently, and every reason to distrust them. Why should they assume that the cops in their town are any better than Uvalde's? They're going to hear "your kid can't have their phone in our school" and think of this.
