The students were sent into the restroom.
A man with a megaphone stood Monday evening near St. Andrews United Methodist Church and called out the names of surviving children. Parents waited nearby, hoping to hear their sons' and daughters' names.
Don Denton hadn't heard from his two sons since the tornado hit the town, but the man who has endured six back surgeries and walks with a severe limp said he walked about two miles as he searched for them.
As reports of the storm came in, Denton's 16-year-old texted him, telling him to call.
"I was trying to call him, and I couldn't get through," Denton said.
Eventually, Denton said, his sons spotted him in the crowd. They were fine, but upset to hear that their grandparents' home was destroyed.
As dusk began to fall, heavy equipment was rolled up to the school, and emergency workers wearing yellow crawled among the ruins, searching for survivors.
Because the ground was muddy, bulldozers and front-end loaders were getting stuck. Crews used jackhammers and sledgehammers to tear away concrete, and chunks were being thrown to the side as the workers dug.
Douglas Sherman drove two blocks from his home to help.
"Just having those kids trapped in that school, that really turns the table on a lot of things," he said.
A map provided by the National Weather Service showed that the storm began west of Newcastle and crossed the Canadian River into Oklahoma City's rural far southwestern side about 3 p.m. When it reached Moore, the twister cut a path through the center of town before lifting back into the sky at Lake Stanley Draper.
Oklahoma City Police Capt. Dexter Nelson said downed power lines and open gas lines posed a risk in the aftermath of the system.
Monday's powerful tornado loosely followed the path of a killer twister that slammed the region in May 1999.
The weather service estimated that Monday's tornado was at least a half-mile wide. The 1999 storm had winds clocked at 300 mph.
Kelsey Angle, a weather service meteorologist in Kansas City, Mo., said it's unusual for two such powerful tornadoes to track roughly the same path.
It was the fourth tornado to hit Moore since 1998. A twister also struck in 2003.
Lewis, who was also mayor during the 1999 storm, said the city was already at work on the recovery.
"We've already started printing the street signs. It took 61 days to clean up after the 1999 tornado. We had a lot of help then. We've got a lot of help now."
Monday's devastation in Oklahoma came almost exactly two years after an enormous twister ripped through the city of Joplin, Mo., killing 158 people and injuring hundreds more.
That May 22, 2011, tornado was the deadliest in the United States since modern tornado record keeping began in 1950, according to the National Oceanic and Atmospheric Administration. Before Joplin, the deadliest modern tornado was June 1953 in Flint, Mich., when 116 people died.
Associated Press writers Sean Murphy, Nomaan Merchant and Sue Ogrocki contributed to this report.