Sitting with students and parents on Wednesday — including some students who were at Marjory Stoneman Douglas High School last week when a shooter killed 17 people — President Trump explored possible ways in which mass shooting incidents at schools could be prevented.

Among them? Arming teachers.

“A lot of people are talking about it — it’s certainly a point that we’ll discuss,” Trump said. “But concealed-carry for teachers and for people of talent — of that type of talent — so let’s say you had 20 percent of your teaching force. Because that’s pretty much the number, and you said it — an attack has lasted, on average, about three minutes. It takes five to eight minutes for responders — for the police to come in. So the attack is over. If you had a teacher with — who was adept at firearms, they could very well end the attack very quickly.”

In the abstract, adding armed staff to schools does seem as if it could help curtail mass shooting incidents. Not prevent them, mind you; even Trump’s aim in that quote is ending mass shootings faster, not preventing them. That difference echoes a report prepared by the National School Shield Task Force in 2013. That document, funded by the National Rifle Association, similarly argued that incidents in which other armed individuals had been able to confront school shooters resulted in fewer deaths.

It’s worth considering, though, what Trump is proposing. What does it mean in economic terms for one out of every five teachers to be prepared to engage with an armed individual intent on murdering students at a school? Or, if you prefer, a proposal from former House speaker Newt Gingrich to hire “six to eight” guards to patrol every school. What’s the tab for that?

A fifth of teachers

Data from the Department of Education indicates there are an estimated 3.1 million public school and 400,000 private-school teachers in the United States. In total, there are about 3.6 million teachers.

One-fifth of that total is 718,000a bit fewer than the number of people in the Army and the Navy combined as of last December. We would essentially be adding 50 percent to the size of the military by mandating that nearly three-quarters of a million people be trained and prepared to take up arms to defend civilians.

The first cost that needs to be considered is training. What sort of training would be required isn’t clear. Do we want to simply teach the teachers how to target an individual and fire a weapon? Or do we want something more expansive?

Let’s say we want the bare minimum, just enough to pass the safety requirement for gun ownership. In Maryland, there’s a company that will charge you $100 for that training. The cost, then, would be about $71.8 million for all of our teachers.

There are groups that offer training specifically for teachers facing active-shooter scenarios. One is the Ohio-based Faculty/Administrator Safety Training & Emergency Response program (FASTER) run by the Buckeye Firearms Foundation. Its program is free for teachers, funded by corporate and individual donors. It includes 26 hours of training over three days and purports to “allow teachers, administrators, and other personnel on-site to stop school violence rapidly and render medical aid immediately.”

In an email to The Washington Post, the group’s program director, Joe Eaton, said that the cost of the training is about $1,000 per trainee. It covers more than just a scenario in which a shooter is on campus, mind you, but that is part of the program.

That more robust training means that the cost for our 718,000 teachers spikes to $718 million. There would almost certainly be some efficiencies of scale that would come into play here — systems would be developed to train teachers quickly and at less cost — but the figure would still likely run into the hundreds of millions of dollars.

Assuming that this particular school supply is covered by districts, we need to account for the cost of the firearms, as well.

Let’s consider the Glock G17, which the manufacturer touts as the world’s most popular pistol. It runs $500 apiece, meaning that our price tag for arming our teachers just went up by $359 million. Maybe Glock, too, would give the Department of Education a discount, perhaps cutting the price in half. That changes the total to $180 million.

Our grand total? If we assume the cheapest training and the discounted Glock, we’re at $251 million to arm 718,000 teachers. If we instead assume the full-price, more expansive training and the full-price firearm, the tab creeps past $1 billion.

Update: At about the same time this article was published, Trump took to Twitter to explain his comments.

If the schools are providing only the guns and not the training, the costs obviously come down — though it seems likely that you would need to either recruit a lot more military veterans to teach or train a lot more teachers to shoot in order to reach Trump’s 20 percent density goal.

It’s also worth noting that “giving teachers concealed guns” doesn’t seem to conflict with “give teachers guns.”

Six to eight guards

What about Gingrich’s proposal? How much would that cost?

As of the 2013-2014 school year, there were about 132,000 public and private schools in the United States, including about 24,000 public high schools. Six to eight guards in those schools means between 791,000 and 1 million guards in place — a bit lower than the size of the armed forces.

To figure out the cost of guarding those schools, we need to know how much those positions would cost. A 2013 analysis of adding armed guards to schools completed by professor Ned Hill of Cleveland State University estimated that school resource officers would run between $75,000 and $97,000 annually. That’s about $80,000 to $103,000 today.

The cost of those officers, then, would run between $63 billion (six guards per school at $80,000 a year) and $109 billion (eight guards at $103,000).

Let’s assume, though, that we don’t need as many guards in non-high schools. Still some, of course; since 2000 there have been at least 61 shootings at elementary and middle schools in the United States in addition to at least 68 shootings at high schools. If we weight the number of guards needed toward older students, we need between 367,000 and 490,000 guards and the range of costs ends up between $29 billion and a bit more than $50 billion.

Hill’s analysis, incidentally, estimated that fewer guards were needed — about 156,000 total — and calculated a price tag of between $12 billion and $15 billion.

Annually.

Other considerations

This is also not a comprehensive look at the costs involved. There’s ammunition, for example, and the costs of annual training programs or hiring new teachers and guards.

And, of course, there’s insurance. Insurance rates increase when armed guards are hired. Why? In part because the risks of accidents also increase.

“When insurers evaluate the use of armed officers, they quite often see risks outweigh the benefits for the average company or organization,” Tory Brownyard wrote for Security magazine in 2013, “risks that have a significant impact on both the availability and cost of insurance coverage.” Some insurers recommend against armed guards entirely.

The added cost is hard to estimate without knowing what schools currently pay, but the increase would likely not be minimal.

What none of the figures above include is the psychological cost of arming teachers. After Trump’s statement was reported, some weighed in on social media.

Certainly some teachers would embrace the idea of arming and preparing themselves — FASTER has a steady stream of clients — but many wouldn’t. Others noted that schools are already strapped for resources, and questioned whether adding firearms and training to the mix made sense.

Remember: These costs would ultimately trickle down to taxpayers. About 100 million taxable returns were filed with the IRS for the 2015 fiscal year, 41.5 million of which were from married couples filing jointly. This is a rough division, but it suggests that the price of arming teachers would cost 121 million taxpayers between $2 and $9 to train and arm a fifth of the America’s teachers (excluding the other costs above) or between $96 and $900 annually for six to eight armed guards to be stationed in schools.

To prevent what, despite the attention these tragedies receive, are still happily rare incidents.

This article was corrected with the proper figures for the number of teachers.