The phrase that’s been drummed into my head is Run/Hide/Fight. So flee first, if possible and only then hide, including barricading or locking the door.
I think part of the issue is that implicit in “flee” in some trainings is “…if you can, know it’s safe and where to”. Especially with young children there will be a hesitancy to take the chance on their running into the danger. Also for instance in my workplace in the case of active shooters, if we are IN our offices, the instructions are to barricade in place because most of the offices are NOT immediately adjacent to an exit.
CNN had a better article yesterday:
https://www.cnn.com/2022/06/07/us/uvalde-school-teacher-arnulfo-reyes-interview/index.html
Good to know I pay as good attention to this as all other work training! 
Even though it didn’t work in this case, I can’t criticize him for telling his students to “pretend to be asleep”. Maybe it has worse odds in general, but young children are likely to be much better at pretending to be asleep than at fleeing.
Most charitably, “pretending to be asleep” has the effect of getting down on the ground and presenting a low profile. Which is actually pretty good as long as the gunfire is only in adjacent spaces. And as noted, the whole run/hide/fight paradigm maybe doesn’t work so well for children.
Here is a new article from The New York Times (gift link) about the police response in Uvalde. A big reason for the delay is that they were trying to get shields to protect the officers.
Thanks for the link.
This article brought up something that I don’t believe I’ve heard or read about previously:
We know that one of the teachers attempted to lock the door from the inside with a key, but did not have the time to do so. We also know that the police were waiting for a key to unlock the door. So the question is: How did the door get locked, or was it even locked during the time the gunman was in the classroom?
As the article says, it may not have been locked.
No one even tried to see if the door was locked?! 
Man, that Arredondo - and the clown corps of the school and local police forces - sound completely worthless. Probably not what taxpayers THOUGHT they were getting for their money!
Heard a bit on the radio yesterday about the big business that is school security. Probably a good business to get into. Essentially endless spending, with no guarantee of any significant benefit.
Mind that all that may not be talking about the same door.
And little chance that you might actually need to act.
Doesn’t that suggest an obvious answer - that the gunman entered the classroom, found the teacher fumbling with a key, and ordered her to lock it.
However, accounts are that the first responders took fire before they retreated. So they may have had the opportunity to push forward and engage before the door was locked. Although if he was shooting through a door cracked open and they only had handguns in those first few minutes, that may have been just pointlessly suicidal.
Really? The obvious answer it suggests to me is that the door was unlocked and the police were a bunch of bumbling idiots.
But they found a key and unlocked it when they eventually did breach, right? So that confirms that it was indeed locked. The BORTAC guys who went in would surely have said “what the fuck” if they discovered that they didn’t even need a key. They are not looking to cover for Arredondo.
Some doors, turning a key to unlock it when it is already unlocked has no effect: the door remains unlocked.
But I suppose it’s also possible that the murderer in this case had time to pry the key from a teacher’s cold dead hands and lock the door himself. I mean, he practically had time to binge watch seasons one through three of Stranger Things while he was waiting for the police to actually do something.
Perhaps, but then again (1) they might have just relied on erroneous reports from local LE that a key was required without checking for themselves (kind of like when you end up standing in a queue that isn’t really for anything just because one person happened to be standing awkwardly in a way that made it look like a line had formed) and (2) just because they aren’t looking to cover for local LE doesn’t mean they aren’t still interested in covering for themselves.
I don’t know why you think that’s necessary. It seems quite plausible to me that he pushed into the room as the teacher was trying to lock the door, and either took the key from her or ordered her to lock it right away, perhaps before shooting anyone in the classroom if he was shooting back at the cops.
For those who are curious about why Chief Pete Arredondo might possibly not have had a radio … he did … until he didn’t:
In his first interview since the Robb Elementary School shooting, the man widely seen as responsible for the delayed police response told the Texas Tribune that it had been a deliberate decision to abandon his primary tool of communication with dozens of other officers before entering the school building on May 24. The choice to ditch his radio, Uvalde school district police Chief Pete Arrendondo said, was tactical—he believed carrying his radios would slow him down or hit him as he ran. “I’ve never heard anything like that in my life,” police tactics expert Steve Ijames told the Tribune, explaining that officers are trained to take their radios everywhere.
I lost more money than I care to admit by having picked “his dog ate it.”
I’m wondering what the odds are that we’ll soon learn that he and his officers also abandoned their firearms due to the possibility that “these things could really hurt somebody.”
Many a time, I’ve seen a crowd of people all standing around outside of an unlocked classroom door, because each of them assumed that someone else had already tried opening it and found it locked.
But those were all students, and there wasn’t any sort of emergency that made it really important to get into the classroom.
And once the border patrol guys did have the key, they probably put the key in the lock and turned it, before checking the knob, because they were already told it was locked, and they had the key, so why wouldn’t they unlock it?
I don’t know why you are all assuming the worst about the police. It’s not like they’ve given us any reason to.