A group of students was watching a Disney movie as part of their year-end celebration when the Texas school shooting began, says a teacher: report

• Students were watching a Disney movie when the Texas shooting began, a teacher told NBC News.
• The kids knew it was not a drill when the teacher ordered them to stay under their desks, she said.

A group of students was watching a Disney movie when gunfire began at Robb Elementary School on Tuesday, a teacher told NBC News.

Speaking to the outlet on condition of anonymity, the teacher said that her students had been enjoying the film on Tuesday morning as part of their year-end celebration. Then, shooting exploded down the hall.

Immediately, the teacher ran to lock the classroom door and ordered the kids to stay under their desks, per NBC.

"They've been practicing for this day for years," the teacher told the outlet, referring to their active shooter exercises. "They knew this wasn't a drill. We knew we had to be quiet or else we were going to give ourselves away."

It was the "longest 35 minutes of my life," she told NBC, describing the wait that followed.

When some of the students began crying, she signaled for them to sit with her, and held them, per the outlet.

Once police arrived and broke the classroom windows, the teacher got the students to line up the way they do daily for lunch and recess, per NBC. She also held the children's hands and helped them out the window.

"After the last kid, I turned around to ensure everyone was out," the teacher told NBC. "I knew I had to go quickly, but I wasn't leaving until I knew for sure."

In the aftermath of the shooting, some parents texted the teacher to express their gratitude.

"But it's not just their baby," the teacher told NBC. "That's my baby, too. They are not my students. They are my children."

The Robb Elementary School shooting, which has left at least 19 children and two adults dead, is the deadliest elementary school mass shooting since the Sandy Hook Elementary School massacre in 2012.