WARNING: Some readers may find elements of this story graphic and distressing.
Children who survived the shooting have described what happened inside the school during the mayhem.
To survive the nightmare, Miah Cerrillo, 11, smeared her friend's blood all over herself and played dead, she told CNN.
Miah and her classmates were watching the movie "Lilo and Stitch" when teachers Eva Mireles and Irma Garcia got word of a shooter in the building. One teacher went to lock the door, but the shooter was right there – and shot out the door's window, Miah said.
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As her teacher backed into the classroom, the gunman followed. He then looked a teacher in the eye, said "Goodnight," and shot her, the girl recalled.
And then he opened fire, shooting the other teacher and many of Miah's friends. Bullets flew by her, Miah said, and fragments hit her shoulders and head.
The gunman next went through a door into an adjoining classroom. Miah heard screams and more gunshots. When the firing stopped, the shooter started playing music that was "sad, like you want people to die," the girl said.
Scared he would come back to kill her and her few surviving friends, Miah put her hands into the blood of a slain friend lying next to her and smeared herself with it, she said.
The girl and a friend managed to grab a dead teacher's phone and call 911 for help, she said. She told a dispatcher, "Please send help because we're in trouble."
The pair then lay down and played dead.
Survivors fear returning to school
Another student in a different classroom, 10-year-old Jayden Perez, said when he and his classmates heard gunfire, his teacher locked the door and told them to "hide and be quiet."
Jayden said he was hiding near the storage area for backpacks during the shooting. Others in his class were under a table. The entire time, he wondered what was going to happen to them.
"It was very terrifying because I never thought that was going to happen," he told CNN. "(I'm) still sad about some of my friends that died."
During his interview with CNN, Jayden started listing the names of friends who were killed. Then he stopped, looked at a row of crosses behind him bearing their names and said, "Basically all of them."
He does not want to go back to school again.
"No, because after what happened. I don't want to. I don't want anything to do with another shooting or me in the school," he said. "And I know it might happen again, probably."
Edward Timothy Silva, a second-grader at Robb Elementary, also worries about returning after summer break.
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"It breaks my heart," his mother, Amberlynn Diaz, told CNN's Laura Coates. "I just don't want him to be afraid of school. I want him to continue learning and not be scared of going back to school. I want him to have a normal life again."
Edward, in a classroom close to the one where the fatalities occurred, heard "loud noises," he said. "Kind of like fireworks."
A woman who works for the school told him and his classmates to hide, he said, as the lights were turned off inside of the classroom.
He and his classmates had been having active shooter drills since they were in kindergarten, he said. On Tuesday, "I learned that we were having a real drill," he said.
Some of his classmates in the room were crying, and he prayed, Edward said. "I was praying, thinking: Why is this happening?"
Diaz said she was told the shooter was next door to her son's classroom.
"That's when I completely lost it," she said.
It was 40 long minutes before she found out that he was safe.
"I had to rush over there to make sure," she said. "I had to see him to believe them."
Now, Edward is sleeping with his parents again, and he is afraid of guns.
"I'm scared someone might shoot me," he said.
