I want to make it clear that I am completely in favor of increasing security with methods other than egress.
I just think it's basically a pipe dream. Any passive system to deny entry that you can propose is not that difficult to defeat if you have time to plan - and an aggressor has as much time to plan as they want. To make passive systems work, someone motivated and vigilant has to be managing all of the passive systems and able to respond to keep them from failing or when they fail to contain the threat by themselves. Someone like this is not cheap, and it will probably take more than one. You have to pay them thousands of dollars a year... every year... forever... It's not just a one-time deal like passive systems.
A fence? Sure, but someone motivated and vigilant has to be watching it, or someone will cut through, ram through, dig under, use a ladder, etc.
Single entry? Sure, but any normal door can be breached relatively quickly with the right tools - I can think of a dozen ways breach a sturdy door, people who open the door can be ambushed (somebody has to take the trash out eventually...), or people are careless and leave it open. And then, a single entry door can be blocked to stop emergency responders. Single entry is a great tactic - but someone has to be actively watching and defending for that to work.
Metal detectors? Security cameras? Guard dogs? A central command center to monitor the school and isolate the threat? Yes, yes, yes, and yes, but someone motivated has to be there to make them work.
How much does a good security team cost annually? Because one stereotypical rent-a-cop won't cut it. And then, when you have a security team, they will be called upon to deal with troublesome students, and subsequently sacrificed to appease irate parents. Our culture will not be willing to pay for the kind of people who would take the job seriously, would not support them when they do their jobs, and a school is not a place that our culture will accept the kind of rigid security you could get away with at a normal "secure facility". Security and convenience have an inverse relationship, and our culture is all about convenience.
Is the building code a place to address any of the above? Should it be? I want all of the security listed above to be implemented, but I don't think it ever will be implemented effectively.
The building code already deals with egress, which is why I got started on this line of thought. In my opinion, multiple egress paths is the only passive system that the victims can utilize to save their life whether help is on the way or not. It is also the only place I am aware of that the building code intersects with school security already. If there are other places that I am overlooking, please comment. I would be interesting in making those code changes as well.