Whoa there pardner.
I went to public school. You probably did too. It was the norm to prop open doors on a hot day. No A/C, or A/C shut off to save money. Probably same here, in a tiny little one-horse town. So yes, the policy that no-one followed was violated. And also yes, if the door wasn’t propped open the kids inside would’ve been sweltering and bitching.
That being said, the principal, deans, and counselors all should’ve been running around campus ensuring it was secured the second after that first shot rang out - they had at least 10-12 minutes to do so. They didn’t. That’s where the adults failed the kids.
They had exactly 5 minutes. Truck crash at 11:28, followed by shots at the funeral home people. Teacher runs back inside and may or may not have gotten door closed properly. Her 911 call was 11:30, shooter enters by same door at 11:33.