That would probably be okay, were we to be living in a police state. When my children were in school, I would not want them in a place that resembled a bunker. My preferred solution to this, in the short term, is to randomly arm teachers and administrators. In the long term, restore mental institutions and bring God back to school and society. Satan is expert at filling a void.
It’s possible to hardened without looking like a bunker.
But, we had a bunker once as an HQ building.
It was so cool. Little bit of it above ground, and the remainder stretched out over half an acre. Hallways, ventilation, cheap air conditioning, heat, etc. (Schools could save utilities money big time.)
Always made me want an underground house. :>)