You still don’t get it, do you?
I was a university police officer. This was long before Columbine but not all that long after the University of Texas Tower incident.
Young people aren’t stupid. This is one of the things that makes securing firearms from teenagers especially challenging and makes securing schools such a problem.
I read the initial findings of the Florida state commission investigating the Parkland shooting. Nikolas Cruz knew and exploited multiple security weaknesses at Marjorie Stoneman Douglas High School. While Cruz committed the murders, the Broward County Public Schools, the Broward County Sheriff’s Office and the administration at Marjory Stoneman Douglas High School enabled him. They made it possible for him to purchase seven firearms and pass multiple background checks. Even though he had been expelled, he was allowed to enter the campus with a rifle case, passing through a gate that was supposed to be secured, and a school monitor didn’t question his presence. The fact that the FBI ignored two tips about Cruz was just icing on the cake and Deputy Scot Peterson’s actions were the cherry on top.
If metal detectors were infallible, TSA checkpoints wouldn’t fail so many tests. The Internet offers multiple sources for tips on defeating metal detectors and tricking the people that man them.
Incidentally, the state of policing in Chicago public schools is a mess. I am not sure how much confidence I would have in using them as an example of success.