Looked Post 16 over for a place to put one but, nope -- all dead serious, Uh.
No, bag checks don’t work well. At all. ‘nuff said.
Maybe you have done this. Illuminate, eh? The kind of protocol on the sites I've seen wouldn't permit a long gun get near the entrance.
Never mind what happens when an attacker say “here it is” and starts shooting.
How did the gun(s) and ammo get into or past a secure entry point? Adam Lanza's scheme depended on an unattended and unsecure door. So did James Holmes' Aurora theater shooting in July, and the Columbine spree.
The school problem is that of bunching up in a dedicated site, requiring a different protocol than that of safeness for free movement in the general open population.
Then there was the case where a kid pulled a fire alarm, then went outside, grabbed a hunting rifle, and shot people as they left the building. Lots of people.
Shotguns have been snuck onto airplanes.
Checkpoints are shooting galleries waiting to happen, having so many people bunched up in such a small place (a TSA disaster waiting to happen).
Many rifles can be broken down to small packages.
Never mind everything already in the building which can be abused.
And no I’m not going into details. Suffice to say its not hard to beat bag checks, and if that’s the centerpiece of your school security a whole lot of people are going to die.
In contrast, many school would-be mass killings have been averted by armed staff and students. Not hypothetical.