Not sure about the armed guards but I do know that there are teachers that are. My kids went to Catholic school here. The only way in is at the front door and you were on video as they asked what you were doing there.
My main concern for teachers is they have enough trouble getting funds for supplies used in the classrooms. Paper towels, soap, sponges, disinfectants, cleaning solutions, A/B wipes, hand sanitizers, etc., things needed to actually be teachers. Im hard-pressed to believe schools will be given firearms and ammo budgets. And to fill the role that we are talking about, they have to be better than the average cop. A lot better trained and thats not to say cops are not trained but have to have training beyond what a cop receives, more along the lines of HRT (Hostage Rescue Team Training). Teachers will be placed in a more tense situation than when the cops arrive.
Lets say someone starts shooting. Cops are called, takes them some time to drive there. Eventually they reach the school and make entry. During the lag, things stabilize. Kids find cover, school gets locked down and kids are evacuated. Maybe the shooter runs out of ammo and kills himself. Unfortunately teachers dont get that luxury.
When the shooting starts they are already there. When they step out into the hallway its not empty. There are kids running around frantically, in a panic state. If they get a bead on the assailant they cant miss. if they miss in all likelihood they are hitting a student.
So they have to be good at it, real good at putting the bullets where its needed. Once they get to that point they have to function properly while on the move and while kids are running in front of you. They have to change their entire mindset. When they are moving thru the hallway they are no longer teachers. They are warriors. They are no longer worried about students. They are worried if a nook is adequate cover. It changes everything.
When they start training for these situations it has to be done in secrecy. The moment a student finds out the teachers are done. Its over. Any effectiveness they had is now gone.
Contrary to popular belief an armed teacher isnt going to be a deterrent. Even with armed guards it isnt a deterrent. If a shooter knows the school has armed guards or armed teachers they will be #1 on the kill list. It is not practical having armed guards/ armed teachers. To keep ammo in the classroom in case a shooter is on campus is insane. And awfully expensive. When the shooting starts teachers need to lockdown their classrooms and save the 30-35 lives of kids. Everyone else is on their own. Forget about looking for the guy. You have to wait for him to come get you.
If its a school that has wings that can be locked down, maybe you will be able to save everybody. Maybe.
Even in that scenario schools are meant to be inviting. There is a lot of open space. So that means there isnt a lot of cover. There isnt a lot of things to hide behind. You cant stay in the open trying to engage the shooter. You will surely get shot, die. The shooter has the initiative. Forget about going thru the hall ways.
Im not a security expert so I consulted with 2 family friends who are retired law enforcement and another who is a retired Lt. Col US Army MP.