NEWTOWN, CONN. - In a first-grade classroom, teacher Kaitlin Roig heard shots.
She immediately barricaded her 15 students into a tiny bathroom, sitting one of them on top of the toilet.
She pulled a bookshelf across the door and locked it. She told the kids to be "absolutely quiet."
"I said, 'There are bad guys out there now. We need to wait for the good guys,'" she told ABC News.
"The kids were being so good," she said. "They asked, 'Can we go see if anyone is out there?' 'I just want Christmas. I don't want to die, I just want to have Christmas.' I said, 'You're going to have Christmas and Hanukkah.'"
One student claimed to know karate. "It's OK. I'll lead the way out," the student said.
As the close-knit community of Newtown, Conn., reeled in the aftermath of one of the worst mass shootings in U.S. history, terrifying new details emerged Saturday about how teachers and staff members at Sandy Hook Elementary scrambled to move children to safety as the massacre began.
Maryann Jacob, a library clerk, said she initially herded students behind a bookcase against a wall "where they can't be seen."
She said that spot had been chosen in practice drills for school lockdowns, but on Friday, she had to move the pupils to a storage room "because we discovered one of our doors didn't lock."
Jacob said the storage room had crayons and paper that they tore up for the children to color while they waited.
"They were asking what was going on," she said. "We said: 'We don't know. Our job is just to be quiet.'" But she said that she did know, because she had called the school office and learned that the unthinkable had happened just steps away.
Meanwhile, someone turned the loudspeaker on, so everyone could hear what was happening in the office.
"You could hear the hysteria that was going on," fourth-grade teacher Theodore Varga said. "Whoever did that saved a lot of people. Everyone in the school was listening to the terror that was transpiring."
Gathered in another room for a 9:30 a.m. meeting were Principal Dawn Hochsprung and school therapist Diane Day along with a school psychologist, other staff members and a parent. They were meeting to discuss a second-grader.
"We were there for about five minutes chatting, and we heard Pop! Pop!, Pop!" Day told the Wall Street Journal. "I went under the table."
But Hochsprung and the psychologist leaped out of their seats and ran out of the room, Day recalled. "They didn't think twice about confronting or seeing what was going on," she said.
They were shot as they tried to tackle gunman Adam Lanza, 20, "in order to protect her students," the school superintendent, Janet Robinson, said Saturday.
Meanwhile, the school's lead teacher pressed her body against the meeting room door to hold it shut because the door didn't have a lock, Day said. That teacher was shot through the door in the leg and arm. "She was our hero," she said.
Robinson said one teacher had helped children escape through a window. Another shoved students into a room with a kiln and held them there until the danger had passed.
A custodian ran around, warning people there was a gunman, Varga said.
"He said, 'Guys! Get down! Hide!'" Varga said. "So he was actually a hero."
In the gym, crying fourth-graders huddled in a corner. One of them was 10-year-old Philip Makris. "He said he heard a lot of loud noises and then screaming," said his mother, Melissa Makris. "Then the gym teachers immediately gathered the children in a corner and kept them safe."
Another girl who was in the gym recalled hearing "like, seven loud booms."
"The gym teacher told us to go in a corner, so we all huddled and I kept hearing these booming noises," the girl, who was not identified by name, told NBC News. "We all started -- well, we didn't scream; we started crying, so all the gym teachers told us to go into the office where no one could find us."
An 8-year-old boy described how a teacher saved him. "I saw some of the bullets going past the hall that I was right next to, and then a teacher pulled me into her classroom," said the boy, who was not identified by CBSNews.com.
Student Brendan Murray told WABC-TV it was chaos in his classroom at first after he heard loud bangs. A police officer came in and asked, "Is he in here?" and then ran out. "Then our teacher, somebody, yelled, 'Get to a safe place.' Then we went to a closet in the gym and we sat there for a little while, and then the police were knocking on the door and they were, like, 'We're evacuating people' ... so we ran out."
The Rev. Robert Weiss recalled the reaction of the brother of one of the victims. "They told a little boy it was his sister who passed on," Weiss said. "The boy's response was, 'I'm not going to have anyone to play with.'"
The New York Times contributed to this report.