RIFLE, COLO. - Kyle Mickelson survived the deadly shootings at Columbine High School as a freshman to try to teach his students school violence can happen to them if they aren’t tolerant.

Mickelson teaches social studies at Rifle Middle School and spent Monday, April 20 - the 10-year anniversary of the then-worst school shootings in U.S. history - explaining what happened and what he did.

“If just one kid changes their attitude, it’s totally worth it,” he said after one of four Powerpoint presentations on the tragedy he showed students that day.

Mickelson said he has come to terms with what happened at Columbine, where a dozen students and one teacher were killed by two other students, who then shot themselves. Mickelson ended up in a science room during the shootings with injured teacher Dave Sanders, who was shot early in the incident but survived until just after most students were rescued.

“I remember everything about that day,” Mickelson said as he began to recount April 20, 1999, when he was a 15-year-old freshman among some 2,000 classmates.

The first indication that something might happen came during the school’s announcements via closed-circuit TV. Each day’s announcements ended with a quote, Mickelson said, and that day the quote was “You shouldn’t be here today.”

“It turns out the gunmen had put that quote in their,” he said. “They had actually given plenty of warning, telling their dates at the prom that something was going to happen and how much better things will be when everyone was dead. But no one took them seriously. We all felt completely safe and never thought that what happened would happen at our school.”

Sanders told Mickelson and several hundred students in Columbine’s cafeteria to first get under the tables and then to run as the gunmen started walking down the halls and shooting. He was shot but helped by some students who knew first aid, Mickelson said.

“We had a dry erase board and one kid wrote ‘1 bleeding to death’ and put it in the window for the cops to see,” he added. “For the next three hours, we just sat on the floor and waited.”

Another teacher helped keep the students in the room calm, even as one of the gunmen walked by the room but didn’t open the door, Mickelson said.

Sanders, despite his wounds, “never worried about himself,” Mickelson said.

“All he said was ‘get these kids out of here’ and ‘tell my girls I love them’,” Mickelson said.

Sanders died about five minutes after Mickelson and all the other students in the room escaped with the help of SWAT officers.

As Mickelson ran to where police said was a safety zone, he saw one dead body, a fellow student.

“I still kept running, but I didn’t know I was running,” he said. “It didn’t feel like it.”

When summer began, Mickelson said he was sure he wouldn’t go back to Columbine in the fall, but changed his mind. On the first day, parents and others formed two long human chains by holding hands as Columbine students walked down the middle.

“That was one of the greatest days of my life and I think it really sent a message that the gunmen didn’t win,” Mickelson said.

Columbine’s principal then and now, Frank DeAngelis, Sanders and other Columbine teachers inspired Mickelson to become a teacher. He’s been at Rifle Middle School for three years.

Mickelson showed students the remains of his melted backpack, which was hit by a pipe bomb after he left it in the cafeteria.

“Two tables down from me where two propane bombs in a duffle bag,” he said. “No one knew they were there. The timers malfunctioned so they didn’t go off. That’s what the gunmen wanted. They wanted them to explode and they’d be waiting outside to shoot survivors as they ran out.”

“I’m sharing this with you guys because you’re going to be freshmen next year at Rifle High School,” he told students. “After the shootings, we realized why does everyone have to hate each other for the smallest things? I don’t want something tragic to happen to you guys, so you need to treat each other right.”

Mickelson said he hoped “the class of 2013 will stick together.”

“It scares me to see what you fight about,” he told students. “The little things I write you up for can turn into something like this. You never know what someone is capable of doing. This can happen at Rifle High School, this can happen at Coal Ridge High School or Rifle Middle School.”