I don't know the exact training they will receive from the police, but I would imagine it would include some sort of hostage/active shooter training, and how to appropriately use a firearm in those situations. It seems they are being trained as a response to these school shootings, so I would expect their training to include how to respond to a school shooter. You're right that most teachers and administrators would not have this kind of training already, but they would presumably be getting it from the police before being permitted to carry in schools.
I fully understand the argument that teachers have plenty of other things to be doing with their time without worrying about weapons training, etc. That's why I would never support forcing teachers to be armed. To my knowledge, it's only those who volunteer that will receive this training and be allowed to carry a weapon, so they're not being forced or coerced into this
So only volunteer teachers/admins will be armed. But will the students in those classes also be volunteers? Cause there's no way my kids are going to be in a classroom with an armed teacher.