Thankfully, random mass shootings at schools are so fabulously rare that you literally don’t need to worry about them. Living in fear of them is like living in fear of shark attacks. Which also means that the “Active shooter drills” you’re talking about are also a complete waste of time. All they do is ratchet up the fear and paranoia.
Which shouldn’t be surprising, because the shooter drills themselves are a result of constant media fear and paranoia, since fear and paranoia gets clicks.