- Video report by ITV News Washington Correspondent Robert Moore
Donald Trump has repeated calls to arm staff at American high schools, saying a teacher "would have shot the hell out of" the gunman who killed 17 people at a Florida school on Valentine's Day.
The US president said recruiting ex-military as teachers who would carry concealed weapons would make schools a "much harder target for attackers".
Claiming teachers would be more likely to protect their students than a guard - a reference to school resource officer Scot Peterson who stood outside the building after the shooting broke out at the Marjory Stoneman Douglas high school - because "they love their students and want to protect them."
Trump's suggestions received rapturous applause from the audience at the American Conservative Union where he was speaking.
“Why do we protect our banks, our airports, our government buildings, but not our schools?" he demanded to loud cheers from the crowd.
Dismissing earlier media reports that he had called for all teachers to be armed as "fake news", Trump said: "I don't want a person who has never handled a gun, who doesn't know what a gun looks like to be armed.
"But out of your teaching population you have 10%, 20% of very gun-adept people. Military people, law enforcement people - they teach. They teach."
Referring to Peterson, Trump said: "I'd rather have someone who loves their students, who wants to protect their students than somebody who's standing outside and doesn't know anybody and doesn't know the students.
"The teachers and the coaches and other people in the building, the dean, the assistant, the principle, they want to protect these kids, and I think we're better with that. It's not all of them. But you have a lot.
"And the beauty is the (weapon) is concealed. No one will ever see it unless they need it. It's concealed. So this crazy man who walked in, wouldn't even know who has it. That's good. That's not bad, it's good."
In an apparent contradiction, Trump also suggested having armed guards outside the school, calculating that a school as large as Marjory Stoneman Douglas would need 150 guards to defend it.
He described the shooting at the high school in Parkland on 14 February where 19-year-old gunman Nikolas Cruz shot dead 17 people, as a "senseless act of mass murder has shocked our nation and broken our hearts."
The president said, that in light of the tragedy, background checks on gun owners would be tightened.
"There's no one who loves the second amendment more than I do, nobody who respects the NRA more, they're friends of mine, they backed us all, they're great people, they're patriots. But we do have to strengthen up, really strengthen up, background checks.
"We don't want people who are mentally ill to be having any form of weaponry. We have to be very strong there."
Earlier in the speech Trump delighted the conservative crowd with a quip about his bald patch after spotting an image of himself on the screen on the wall at the Maryland venue.
Smoothing down the back of his head, Trump said: "I try like hell to hide that bald spot, folks. I work hard at it. It doesn't look bad. Hey, we're hanging in."
The joke was a reference to a video of the president boarding Air Force One in high winds last month that seemed to show a large hairless patch on the back of his head.