Jonathan Blank, Julie Cordover and Carson Abt, survivors of the shooting at Marjory Stoneman Douglas High in Florida, were among those who met with President Trump on Wednesday. (Chip Somodevilla/Getty Images)

Seated between teenage survivors of the Florida school shooting, President Trump said during a White House listening session Wednesday that arming teachers and posting gun-toting veterans in schools could deter or stop school shooters.

Trump talked about strengthening background checks and increasing mental health resources. But his most pointed and specific remarks came when he spoke about adding security to schools by arming teachers.

Trump posited that if Aaron Feis, a popular football coach, had been armed, he could have stopped the gunman who killed Feis and 16 others last week at Marjory Stoneman Douglas High School.

“If the coach had a firearm in his locker when he ran at this guy — that coach was very brave, saved a lot of lives, I suspect — but if he had a firearm he would not have had to run. He would have shot and that would be the end of it,” Trump said.

He then proposed to arm 20 percent of schoolteachers and to hire veterans as armed school guards.

“A teacher would have a concealed gun on them. They’d go for special training and they would be there and you would no longer be a gun-free zone,” Trump said. He suggested that an armed teacher on campus could reach a school shooter faster than responding police officers. “You’d have a lot of people that would be armed, that’d be ready.”

Trump’s proposal to make 20 percent of public schoolteachers ready to fire back at a shooter would mean training and arming about 640,000 people nationwide. The idea was met with swift backlash from teachers’ groups nationwide.

“Bringing more guns into our schools does nothing to protect our students and educators from gun violence. Our students need more books, art and music programs, nurses and school counselors; they do not need more guns in their classrooms,” said Lily Eskelsen García, president of the National Education Association, the largest teachers union. The group represents 3 million educators in K-12 schools and on college campuses.

“We need solutions that will keep guns out of the hands of those who want to use them to massacre innocent children and educators. Arming teachers does nothing to prevent that,” the union president said.

“This is bar none, the worst theory of action I’ve ever heard,” said Shanna Peeples, a former educator who worked in Texas when she won the 2015 National Teacher of the Year award. She shared her thoughts on Twitter. “Texas law allows schools to arm their teachers. That’s not a good thing. None of us are trained to respond to threats in the way law enforcement is.”

Trump polled the room Wednesday, asking who liked his idea to arm teachers. Several people — including the parents of survivors and victims of the shooting at Stoneman Douglas High, who were at the session — raised their hands.

At least two school districts in Texas have armed teachers, both in remote parts of the state. Their superintendents have defended the policies, saying their educators are prepared to respond if a gunman arrives on campus, according to KXAN-TV.

At a town hall hosted by CNN on Wednesday evening, Broward County School Superintendent Robert Runcie, whose district includes Stoneman Douglas High, roundly rejected the idea.

“We don’t need to put guns in the hands of teachers. You know what we need? We need to arm our teachers with more money in their pocket,” Runcie said to roaring applause.

The idea of arming teachers has received a mixed reception among Americans. In a recent Washington Post/ABC News poll, 42 percent of respondents said armed teachers could have prevented last week’s school shooting in Parkland, Fla., while 51 percent disagreed.

Delaney Tarr, a 17-year-old senior who survived the shooting at Stoneman Douglas, said it was impractical to arm schoolteachers.

“There are so many things that could go wrong,” Tarr said. “We are not a prison. We are not a police force.”

But the father of a Stoneman Douglas High student suggested that arming school personnel — even having undercover police officers work as janitors or cafeteria workers — could be the key to stopping a school shooter when other measures fail. Fred Abt pitched the idea to Trump early in the meeting.

“If you can’t stop it from happening — and with hundreds of millions of guns out there, I don’t know if it will ever be fully stopped — the challenge becomes when it starts how to end it as quickly as possible,” Abt said.

A previous version of this article incorrectly identified the room in which the listening session took place. This article has been updated.