The average time LEO spends on the range is 15 hours a... year. Do you really think they spend that much time on the range? Only the highest tier unit trains that much
Yes, they train constantly to be at their best but that amount of range time is indicative of other matters they must train for and attend, not the least of which patrolling all day and almost every day. The job of the infantrymen seemed to be more simple. After all, they don't have to train as medics, remember every law, etc and yet it is not unusual to meet one who hadn't gone to the range to re-qualify in a year.
Now with you as a teacher, I don't know what training you would undergo, but you can take an NRA class for a day. Just two days, in a year. You are given a manual, and it has all the rules for gun safety and handling (all of which are easy to learn and remember). After which you can spend 2-3 hours a month on the range, applying every rule in shooting and safety (and in your free time, at home, can do what's called "Dry-Firing". Applying the fundamentals of marksmanship with an empty chambered gun. All safety rules apply, including Ammunition to always be stored in the other room).
Furthermore, I don't believe you're expected to train to either levels as your duty as a teacher, is first and foremost, to protect your students. That means staying, as a Shepherd, with your flock, until the danger passes (in this case, an All-Clear announcement). If in the classroom, you just have your students behind you, and guard the door (after the door is barricaded). If they're on the playground, you shepherd them out.
What you're not supposed to do, is to leave your flock to hunt for the wolf when there might be others about, yes? Let the Police do their job.
"Police firearms training: How often should you be shooting?" By Dave Grossi Jun 23 2011 PoliceOne
https://www.policeone.com/police-training/articles/3738401-Police-firearms-training-How-often-should-you-be-shooting/