Somehow, her phone rang. It was her mother, and she told her to call 911.
There were no more walls left in her school. The bumper of a car sat between the pre-kindergarten and kindergarten students.
"I could see the kids peeking around what used to be a corner," Simpson said.
Justin Ayres, a fifth-grade teacher who was the first to spot the twister, was the first one out on one side of what had been the school. Men and women, meanwhile, were running foward to help.
Within minutes, Simpson recalled, the pre-K, kindergarten and first graders were safely out. Her husband soon arrived and put his hand on her shoulder.
"I said, 'Go help second and third grade,'" referring to those students who were in a different, nearby building. "I haven't seen any of them yet."
More and more students emerged, some of them heading to a nearby church. But what had been the second- and third-grade building was precarious, at best.
"I made my way around there, then I begged and pleaded for the human chain to get me up there," Simpson said. "They did. And they were pulling out students and teachers."
All seven killed at Plaza Towers died in that rubble.
"The rest of the evening was a nightmare."
'They grew up really fast'
Briarwood Elementary Principal Shelley Jaques-McMillin's first impression of Monday?
"I remember thinking, "Yeah, it's sunny! So we're going to be able to go outside."
School started, as it always does, with what's called the Grizzly Growl -- a time for singing, dancing, celebrating.
"(I remember) the happy faces, how excited they were, just seeing them smile," said Jaques-McMillin. And there was laughter when a special guest -- a sheep -- made a special appearance. Staffers had to give it a kiss, because a group of students had reached their reading goal.
Lunchtime that day was especially fun.
"This is what school is about," Jaques-McMillin remembered saying at the time. "This is why we do what we do. They're so happy."
The next few hours went by in a blur -- in some ways, much like at Plaza Towers. There were the students and staff doing what they'd practiced in tornado drills -- the sirens, and more.
Jaques-McMillin felt stronger, more resolute this time than when the last EF5 tornado -- the strongest such classification -- came through Moore. When that happened, she was alone and horrified.
This time was different. She had a sense of purpose, beyond simply making sure they survived.
"I have 675 students that I promise their parents every single day, I will protect your kids," Jaques-McMillin said. "I'll feed them, they'll be safe, and I'll give them back at the end of the day."
Briarwood Elementary didn't survive the tornado, but everyone who had been inside did.
They included 4-year-olds and students set to move onto seventh grade, though they were still kids at heart.
Yet on Monday, one of them reached down to a teacher, who was trapped in the rubble with water from a busted pipe blowing in her face.
"He grabbed her hand and said, 'Calm down, I'm going to dig you out."