It's not enough just to place armed security guards in schools. Using some other country as a model and example shouldn't immediately alleviate any concerns. Those schools don't operate the same as American schools. Their security likely doesn't interact with the students the same as placing armed security and even police in schools. Their assignment and rolls appear to be strictly limited to outside enemy threats. We've already witnessed the likelihood of everything that can go wrong will.
There should be strictly enforced rules of what is allowed and what isn't. It's doubtful those schools in other countries with armed security or a military presence are allowed to be involved with the daily discipline of those students. An armed guard, police or security would never get away with body slamming a skinny 11-year-old onto a school hallway floor for being mouthy or getting sassy. Nor would that country put up with such brute tactics.
An armed guard, security or police in those countries where there's armed presence at schools would never be allowed to pick a student up, still sitting at her desk and toss the student clearly across a classroom. Arrest and placed a child in handcuffed for writing "OK" on her desk, or spraying perfume on her own body, after the student had been taunted and bullied and told she "stink."
Armed guards, security or police in those countries would never be called into the school office to stand alongside a tiny sixth grader as an act of intimidation to force the student into admitting to some minor infraction they were never guilty of in the first place. The student stood her ground and refused to lie and admit to something she didn't do even with an 6 ft 9'ner by her side with his gun holstered at his side.
That once sixth grader is now a grown and married woman, with both she and her husband together serving "their country." Her in a supportive roll to him. She came out fine. Others aren't so lucky.
What's often done to America's children never be tolerated in those other countries, and on the rare chance lines are crossed there would be severe consequences no doubt.
Oh, yeah. Back to the questions needing asked:
1. What will the roll of private security be in the schools?
2. What are the consequences when, not if, lines are crossed?
3. Are armed security to be involved in the daily disciplining of students?
4. If so, how so, and to what limits?
The remainder, put your thinking caps on and add some more questions in need of answers.