I don't know how check points or metal detectors would work on many school campuses. The elementary and high schools I attended in Chicago were each one building with main entrances, with the main office right by the entrance. In situations such as those you could institute check points and metal detectors. However, take a look at our schools locally, comprised of numerous buildings spread out over the school's property. There is no one entrance point.
I think Schools, officials and engineers would have to go back to the drawing board and implement security gates and such, limiting the access we are currently accustomed to today. You want to go on campus, you must go through a checkpoint. Removing shoes, phones, belts etc... just like at the airport. Like I said it would be a pain to deal with but I would be willing to abide for the safety of my children and others.
It would also cost a lot to implement these kind of security measures to Schools but I feel like it would be worth it.
Life should not be a journey to the grave with the intention of arriving safely in a pretty and well preserved body,
but rather to skid in broadside in a cloud of smoke, thoroughly used up, totally worn out, and loudly proclaiming
"Wow! What a Ride!"
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