I’m an educator and work out of several P-12 buildings in my role. Offering my thoughts.
It is not common for elementary schools (in my rural and high poverty area) to have armed guards or full-time school resource officers. The SROs from the secondary schools serve the elementaries as needed.
When elementaries have big award events, talent shows, graduations, etc, it is common to have caregivers and families use a side entrance that feeds directly into the award area, like a gymnasium or cafeteria, rather than creating a chokepoint in the usually-small office foyer area. It also limits the visitors to the specific area of use, rather than having 100+ people walking through the core of the school with all the hallways, classrooms, and students. My elementaries (in several districts I've worked in) do not check in caregivers/family or issue visitor badges for these large events. Caregivers/attendees are contained to the area, staff block doors into the non-award areas, and then attendees leave immediately. Edited to add: there would usually be a sign-in sheet for attendees, but that's it.
What I'm wondering about, with the recent MSM news about how long the shooter was possibly shooting outside of the school (WSJ is reporting he was shooting outside the school for 12 minutes), is whether the school was in lockdown with all classroom doors locked. Anytime there is a possible threat near the school, the schools go into lockdown or lock-in protocols, which means no one is leaving their rooms, all the doors are locked, and all windows are blacked out. Once in the building, he should not have been able to enter a classroom without significant effort to get inside. (I’m wondering about the adjacent classroom set up and how that worked. Was it an empty classroom? Was there a retractable carpet wall that separated the rooms or was it a permanent cinderblock wall? Etc)
I’m also skeptical how the shooter knew about that unlocked door. Older buildings typically have lock issues (someone turns their key too many times and doesn’t realize the handle is unlocked, vs a FOB entry system that eliminates user error) or doors that don’t close all the way without being pulled shut, but I wouldn’t count on finding an unlocked door. Most of my buildings are very old and routinely have these issues that are being blasted out through e-mail, but, again, I wouldn't *count* on finding an unlocked door on any random day. IMO, something is up with that.
All MOO. IMO.