That’s about as likely as seeing two people get struck by lightning at once.
To a first approximation, school shootings don’t happen. A fraction of a fraction of a percent of all gun crime, let alone of all murder. And they happen everywhere guns are legal, across Europe and beyond, and even in places guns aren’t legal like the UK, where instead you see improvised explosives used at about the same per capita rate with similar death tolls per instance.
It really is impossible to overstate how utterly insane active shooter drills are.
To reduce casualties (which they won’t) if an active shooter shows up (which they won’t), we inflict absurdly traumatic drills on children starting younger than 8, in hopes that they’re remember some of it (which they won’t).
It’s like if, in order to make kids slightly safer in the event of a car crash, we made them all take a back seat in crash tests twice a year. Even if you’re padding it enough that no one’s physically injured, you’re traumatizing them all, many of them for life, to potentially make them marginally safer in the event of something that isn’t going to happen to them. And that would still be at least an order of magnitude more likely to happen to them than a school shooting! Probably 100x or 1000x!
If you want to protect children from guns, do something about suicide.
That’s by far the most dangerous use of guns; children accidentally injured or killed by someone else committing suicide by gun almost certainly outnumber children killed in mass shootings, just because suicide is so much more common.