The problem with Bullet resistant doors for schools:

Is if the shooter knows that these doors are bullet resistant in the first place. Then a shooter might either go outside and shoot into rooms from the outside (on the first floor) or be a sniper shooting into rooms from the outside somewhere.

But students likely could hide beneath school windows facing the outside where the shooter couldn't see them to target them directly.

However, it is true that getting through a bullet resistant school room door might be so difficult as to give police or swat teams enough time to keep students from being killed in the first place except for the shooter by the police or swat team.

IF you have bullet resistant doors to classrooms and some armed and trained teachers with weapons likely this might be the best outcome for students to stay alive long term nationwide.

But, if you advertise the fact that you have bullet resistant classroom doors for a school as a way to draw more students feeling safe there, you also inform any potential shooters of these doors as well.