So you think your broad, sweeping generalizations comprise a coherent strategy?
Puh-lease.
Most modern public schools are large, spread out buildings and campuses that take several minutes to cross on foot.
If that hare-brained plan were to have a chance to succeed, there would have to be armed teachers all over the school in order to have one nearby when a shooting began.
And of course, the chances are nowadays that the shooter will be wearing body armor which can be easily obtained, while the teacher won't be.
And even if those two situations were dealt with, a shooter bursting into a classroom would have time to rack up a sizeable body count before any armed teacher could secure his/her weapon from its locked, secure location, don their body armor and carefully make their way towards the sound of gunfire, still not knowing exactly which classroom it is coming from.
And during the time that process is taking place, parents and families are having their sons, daughters, brothers, sisters, nephews, nieces and grandchildren, slaughtered by bullets all because a bunch of jackasses who can't get it through their thick skulls that the old west and pioneer days are long gone and most of that good guys vs bad guys shoot 'em up shit was all just Hollywood make believe bullshit to begin with.
THE PROBLEM IS GUNS.
THERE ARE TOO MANY AND THEY'RE TOO EASY TO OBTAIN.
PERIOD.