One case of an armed deputy "hiding outside" isn't real evidence at all. I assume you do realize this.
It has been far more than 1 deputy
So how many attacks have there been in schools with armed security? And in comparison to schools without armed security? Taking account of other relevant factors that will increase/decrease the risks?
The ideal situation would be that armed security would be a deterrence for an attack taking place. (We don't know if deterrence works just by looking at one or two cases.)
For people "hiding outside", you need to know how many attacks have actually taken place when armed security was around, and how they behaved. Not everyone is going to run away right?
"Football coach Aaron Feis died shielding students"
https://www.nbcnews.com/news/us-new...tball-coach-aaron-feis-died-shielding-n848311
So if some people are armed, presumably at least some of them will try to take on an attacker.
Also, how many schools have these school police officers? Are they there every day all the time? Are they always armed?
Here is a case mentioned in the Twitter thread:
"An alert security officer at a Southern California high school helped thwart a potential attack Friday, two days after the deadly Valentine’s Day shooting in Florida that left 17 people dead, authorities said.
The Los Angeles County Sheriff’s Department said they raced to prevent a copycat attack last Friday, acting on a tip from a security officer at El Camino High School in Whittier, southeast of Los Angeles."
https://www.washingtonpost.com/news...guards-tip-police-say/?utm_term=.bf10cba75efa
It's not the same as shooting an attacker obviously. You don't need to be armed to pass on a tip. But it may still be a case of school security stopping a shooting whether or not they were exactly the same as a "school police officer" I don't know.
And:
A school resource officer at Coral Springs High School tracked down a former student who entered the building armed and handcuffed him
https://www.policeone.com/juvenile-...officer-stops-potential-mass-school-shooting/
And:
The rampage might have resulted in many more casualties had it not been for the quick response of a deputy sheriff who was working as a school resource officer at the school, Robinson said.
Once he learned of the threat, he ran -- accompanied by an unarmed school security officer and two administrators -- from the cafeteria to the library, Robinson said. "It's a fairly long hallway, but the deputy sheriff got there very quickly."
The deputy was yelling for people to get down and identified himself as a county deputy sheriff, Robinson said. "We know for a fact that the shooter knew that the deputy was in the immediate area and, while the deputy was containing the shooter, the shooter took his own life."
He praised the deputy's response as "a critical element to the shooter's decision" to kill himself, and lauded his response to hearing gunshots. "He went to the thunder," he said. "He heard the noise of gunshot and, when many would run away from it, he ran toward it to make other people safe."
https://edition.cnn.com/2013/12/14/us/colorado-school-shooting/index.html