The CSO web site has an interesting article on securing a suburban high school. An excerpt:
It was as difficult as it sounds and it required difficult conversations. Everyone agreed, for example, that the school should have smart doors that have magnetic locks and can be controlled by computer. But the police rep rather intensely demanded that the architects’ design allow for complete lockdown of all doors. Lockdown can keep a gunman out, or at least slow him down. Reduce the number of people shot dead.
The fire department rep protested with vehemence. He mandated that doors stay open on each of the school’s four floors at all times. He was imagining the crush of students and teachers trapped in a locked down building during a fire.
[NOTE: I'd add: Early intervention/counseling with troubled children, adopting a tough line on discipline, a willingness to go to court to uphold suspensions and expulsions, and an equally tough stance on bullying. Designing a school is a defensive measure. Defensive measures give the initiative to the offenders. My guess is that fear of lawsuits has greatly hindered school administration.]