I’d think part of the instruction is what to do if the alarms go off and you’re in the hallways, cafeteria, auditorium, etc. People dashing out every exit is kind of the opposite of a lockdown, but people streaming into classrooms is probably a bad idea too.
I've sat through almost 20 years' worth of active-shooter training in schools, and that gets brought up literally every single year. It's been a concern for teachers, admins, and CoPs literally since Columbine:
what do you do if you're outside of a classroom when shit goes down?
There are answers, but none of them are all that good. They amount to, "You've got the rest of your life to find a safe place."
A lot about surviving a shooting incident is just sheer dumb luck. We don't like to admit that, but it's true. I think there are probably good reasons why so FEW school shooters choose to start their rampages during lunch or passing periods, but I don't know enough to claim I know what those reasons are.
Suffice it to say almost all shooters have chosen times when classes were in session.
I’ll make a point of talking with some SROs when I’m working with the PD in the upcoming town elections that precede the November elections to see what they’re thinking. It’s one thing for the FD to respond to a Fire Alarm and another for the PD to respond to an Active Threat Alarm. I’m sure they’ve considered an attacker pulling a Fire Alarm to get the classrooms opened up and everyone in the hall. What a sh*t show to would be for the FD to be responding when the Active Threat System gets activated…
Be prepared to receive a polite non-answer. Because...
1. They're not all that interested in you knowing what they're thinking, because they're cops and you're not, peasant.
2. You're not a teacher nor a school administrator, and your need-to-know is not as great as theirs. Those people will go through training, which will give them a more precise answer than you (a normal, everyday citizen) will get.
3. Yes. They most certainly have considered the PD/FD concern you bring up. Both CoPs and the local Fire Chief talk to us about that very issue every single year. The polite non-answer you get will reflect that, and not go into much more detail than that.
The town where I work is tiny, mismanaged, underbudgeted, and generally shittier than most towns... and even here, the CoP and FD Chief are extremely well-trained and informed about what the local SOPs are for school shootings. Most towns hereabouts are on the same page, because they'll all be responding to each others' crises.