Story highlights 6 kids died from asphyxia, 1 from blunt force trauma, state medical examiner's office says

Teachers tore through the rubble to save screaming students

"I had to hold on to the wall... I didn't want to fly away," one little girl says

The disaster sparked a call for storm shelters in schools

It was the end of the school day. The children at Plaza Towers Elementary School were stuffing their backpacks, looking forward to going home, playing with friends, eating snacks.

But the tornado warnings changed that.

When the twister came barreling in Monday afternoon , terrified young students huddled together in the hallways, screaming as walls and roofs caved in. Chairs and backpacks swirled above them. The winds and blaring sounds enveloped them. Cars from the parking lot landed just inches away.

Teachers dove onto groups of kids to protect them from falling debris.

It was the biggest tornado they'd ever seen. Described as a lawn-mower blade spanning more than a mile, it shredded through their town.

"It was scary," student Julio Rodriguez told CNN. Teachers instructed the kids to crouch down, "and you covered your head with your hands," he demonstrated.

"I had to hold on to the wall to keep myself safe because I didn't want to fly away in the tornado," one little girl told KFOR

A first responder captured this photo at the scene of the devastated Plaza Elementary School in Moore, Oklahoma.

The 17-mile-long twister stayed on the ground for 40 minutes.

By the time it was gone, so was the school in Moore, Oklahoma. In its place was a huge pile of rubble, trapping teachers and children.

And seven students were dead.

They were in a classroom, Moore Fire Department Chief Gary Bird told CNN Wednesday.

Initial reports after the disaster left confusion about exactly how the children had died.

Lt. Gov. Todd Lamb told CNN Tuesday that they were in a basement, where they drowned. But Bird said Wednesday that based on everything he's been told, "it had nothing to do with flooding."

The state medical examiner's office ultimately determined that six 9-year-olds died from asphyxiation, or suffocation, and one 8-year-old died from blunt force trauma.

In many ways, the school became the epicenter of the tragedy in this shattered town, part of the metropolitan Oklahoma City area.

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First responders and volunteers rushed to the scene to begin the treacherous work of searching for survivors.

Local resident Adam Baker told CNN he found some of the dead children in a shallow space.

"The ones that were deceased had bumps, scrapes, and they probably would have made it if they weren't pinned," he said. Pieces of pipe, metal, desks, 2-by-4s, and other debris were on them, he said.

"We had to pull a car off a teacher and she had three little kids underneath her," one first responder, in tears, told KFOR. "Good job, teach."

"I was on top of six kids," one sixth-grade teacher said, working her way across the rubble Monday. "I was lying on top. All of mine are OK."

Teachers helped tear through several feet of rubble to rescue sobbing students, some of them injured.

Rescue teams successfully pulled several children from the leveled school.

Crews continued their search around the clock, rummaging through nearly 40 feet of rubble, CNN affiliate KOKH reported.

Some students were fortunate -- they got out of the school before the tornado struck.

Officials had managed to bus some children to a nearby church, which turned out to be clear of the tornado's direct path, KFOR reported.

After the tornado, terrified parents hurried to get as close to the school as the devastation allowed. They had been helpless during the twister, unable to get to their loved ones, desperate. They were sent to the church to begin what for some would be a horrible wait.

The devastation on psyches is palpable throughout Moore.

"We have not yet reached the coping state," a first responder named Wes told CNN iReport Tuesday "We still have not processed what has happened."

Disaster sparks call for shelters

Even so, the horror has already sparked calls for changes in Oklahoma schools.

Plaza Towers Elementary did not have a storm shelter.

"Most of the schools in Oklahoma don't have one" because of the cost, Moore Mayor Glenn Lewis told CNN. But he said he's sure that will change.

Schools that rebuilt after a massive tornado in 1999 do have storm shelters, he said.

Oklahoma state Rep. Mark McBride called for legislation next year. "The children are sacred. We need to protect these kids," he said.

The state is so used to having tornadoes that people "get lax" and think "it's not a big deal," he said.

Now, McBride added, "it's got to change."