Students and teachers were back in school within a few days, he said, handing out cookies in the space where a gunman tried to kill their classmates; both injured students survived. For a while, it was impossible not to think of it in class.
"You try to get a little bit of effort out of a kid that's basically doing nothing, you can legitimately say 'You know there are people here who would walk through fire for you,' " Benke said. " 'Why aren't you holding up your end?' "
Three years later, it's ancient history for most students, but not for him.
He thinks about it a little every day. He's diligent about locking doors and keeping watch. He can still envision the people he saw standing over him on the ground -- the teachers, parents, bus driver and maintenance worker ready to pounce if he lost his grip on the gunman.
"I finally realized why I kind of get emotional and mist up," Benke said. "It's not because I'm afraid or anything like that. It's because I'm just so damn proud of the people that I work with, and the kids."
Just as in the days after the shooting, a counselor checks with him whenever there's news of a school shooting or even a simple drill that might trigger a traumatic memory.
It's an unusual response, Benke thinks, but then, his district is especially prepared for crisis: His middle school is just miles away from Columbine High School.
In fact, few teachers who witness school violence are offered counseling, said Edward Mooney, a California high school teacher and Northeastern University doctoral student who studies the effect of school violence on teachers.
After disturbing events such as a shooting, many teachers struggle with post-traumatic stress. It can be disabling, and made worse by administrators who want to move on, avoid the topic, "basically the treatment of 'You'll get over it,' " Mooney said.
Mooney has taught for more than 20 years, and with every tale of teachers' heroism -- whether Moore, Newtown or events that hardly make national news -- he worries about how few resources exist for them.
"The teacher feels overwhelming anguish. Those are empathetic, compassionate people," Mooney said. As he wrote his dissertation, he thought of his own colleagues and especially his students. "'What if it happened to him? Or her?' That would shatter me."
A nurturing school climate and support system for teachers who've experienced violent trauma can help, Mooney said, but it seemed like a tough culture to create amid the budget cuts and teacher bashing of the past few years.
"We have this unusual relationship with young people that many other people in professions don't have," Mooney said. "I hope society and districts see that."
Benke, the Colorado math teacher, is on the verge of retirement. After more than 30 years of algebra, he said, it's time to try something new.
He wants to lobby for some changes to teacher certification renewal. He'd like it to include first aid courses or self-defense classes, easy additions he said would cost nothing and keep students safer. He wants legislators to respect teachers for their academic expertise, but also as first responders, who need a clear emergency response protocol. He's writing about what happened in the middle school parking lot, maybe a book.
It was an intense few minutes, he said, but then, teaching is an intense business.
There' no handbook for how to motivate an apathetic middle school boy, to discover a girl abused at home, to know whose mom is dying of cancer, who is smarter than her homework suggests, who responds best to a lecture in the hallway or who needs a hug.
"That's a whole lot more lasting than whether they remember the quadratic formula," Benke said. "I used to think my job was to try to get as much math in kids' heads as I could.
"Then, I realized, what I did was build people."