A Junior ROTC student jumped into action when he heard the gunfire – ushering classmates into a classroom where he used Kevlar sheets to help protect them from the mass killer, according to a report.

Colton Haab, 17, ushered up to 70 people into a JROTC classroom at Marjory Stoneman Douglas High School in Parkland, Florida, as the bullets from an AR-15 flew.

“We took those sheets, and we put them in front of everybody so they weren’t seen, because they were behind a solid object and the Kevlar would slow the bullet down,” Haab told CNN on Thursday.

“I didn’t think it was going to stop it, but it would definitely slow it down to make it from a catastrophic to a lifesaving thing,” the quick-thinking youngster added.

The Junior Reserve Officer Training Corps students use the Kevlar sheets as a backdrop during marksmanship practice. The material is used to make bullet-proof vests.

Luckily, the Kevlar was not needed because the deranged gunman didn’t enter the JROTC room – but Haab said he and a pal had a plan just in case.

“I was a little scared. I was more worried about getting home safe, making sure everybody got home safe,” he told CNN.

“God forbid, if he did come into the classroom. I didn’t want that to happen, but if it did, I would try to stop him with another friend of mine that was with us.”

He added: “We grabbed two pieces of two-by-four, a fire extinguisher and a chair,” Haab said. “We were going to try to stop him with whatever we had,” according to Reuters.

Haab said he saw heroic football coach and security guard Aaron Feis running toward the gunman to help shield the students before he, too, was fatally shot.

“That’s Coach Feis. He wants to make sure everybody is safe before himself,” Haab told CNN.

“He’s definitely in a better place now. I’m glad that he didn’t suffer that much. It’s sad because it’s not going to be the same without him at school anymore.”