Absolutely, but the US have a gun culture that is in direct conflict with this sound proposal.

Another measure would be to raise the punishment for being an accessory, according to https://www.sandyhookpromise.org/blog/gun-violence/16-facts-..., at least one other person had knowledge of the attacker’s plan in 80% of the cases.

I don't think metal detectors or more surveillance at the school will help enough.

But implement the first two measures as a start.