We have a metal detector to go into Court. You cannot get through with anything metal on your person, so you have to take your belt off, and put your phone, change, pens, keys, etc in a bowl, or purse, or bag, and run it through the x-ray machine.
It slows things down, and is frustrating, but it works. If you don’t pass the machines, you don’t get by the deputies.
I don’t know how that works for schools. It may complicate things so much that it would be impractical to try and heard 3000 kids through those machines each morning. But perhaps what you could do is setup a system where the backpack had no metal, mechanical pencils or some non-metallic pen, or small enough metal that it would not set the machine off, drop your phones and keys in a side bowl as you go through, but run every kid through those metal detectors, and have one point of entry with an armed guard or two.
Just some thoughts. My real sermon would be about sin caused these shootings, and rejection of God and the Bible, but really in this case, I think this truly is a kid whose mental competency is at issue. I truly feel sorry for him too because he will leave each day knowing he killed those kids, and that will not change for him here on Earth.
The schools should have at least the same security most police and sheriff offices have.