The boy was persuaded to put down his weapons by three teachers who entered the classroom to talk to him. The incident was over in five minutes and no one was hurt.
Early Show Co-Anchor Jane Clayson spoke with one of the teachers, Fabio Hurtado, and the school's principal, Brother Anthony Cavet.
The student, identified by police as Richard Dalco Jr., walked into his biology class with a 9mm semiautomatic handgun and a black gym bag with a .25-caliber pistol and ammunition.
"This is how we're going to do things," he said, putting down his bag and putting a bullet in the semiautomatic pistol.
He then pointed both guns in the air and ordered teacher Heather Gillingham out of the room, police said. About 30 students remained.
Then the school's staff acted on its emergency training. A secret code went out over the intercom system to alert teachers about the emergency. A fire alarm went off and the school's students were evacuated to the gym.
The three teachers then went to the classroom to talk with Dalco.
Hurtado says the teen "was very scared. He was very emotional. He was crying. He was sorry for what he was doing, but he felt alone. He felt confused ... I knew in his heart he didn't want to do anything wrong. I knew he was nervous. I knew he was upset. I just appealed to his sense of being a human being."
The teacher says Dalco is not a violent kid. He thinks he just wanted to get attention. "I think kids say things, they don't know how to express what they want ... He was depressed and wanted help."
Brother Cavet, the principal, says while the student occasionally saw the school counselor, "there was no way of seeing this coming ... There was absolutely no way we could have predicted this."
He credits the school's crisis plan with helping avert a tragedy. "Other schools probably have plans, but we were under a mandate to get plans in by 2000. We have a lot of fire drills where students must be quiet. They can evacuate the school in one minute and a half. We also have a plan where five faculty members respond to a specific code and go to the scene."
Cavet urges every school to "put an emergency program into effect immediately. A highly finessed one dealing with different types of situations with lock-ins, lock-outs."
But in the end, he says, it was the teachers' courage that saved the day. "The people are more important than the plan. These people who put their lives in danger were more important than that plan."
If there's a lesson to be drawn from this near-tragedy, Cavet says it's that we "understand how precious we are to each other, not only during timeof crisis. It's very important the way we speak to each other with gentleness and with affirmation because we're precious in the eyes of god. We're very important to each other. It shouldn't take a crisis to bring this point out to each of us."