A Robb Elementary School teacher recalled the harrowing moment she heard the sound of gunfire ricochet down the hall when 18-year-old Salvador Ramos allegedly began his rampage.

The teacher, who asked to be anonymous, told NBC News in a Wednesday interview that the ensuing mass shooting where the gunman allegedly killed 19 students and two teachers in another classroom was “the longest 35 minutes of my life.”

She said she heard the unmistakable sound of gunshots erupt as her students were watching a Disney movie Tuesday to celebrate the last week of class when she heard gunfire erupt down the hall.

The teacher quickly shouted for her students to hide under their desks and sprinted to lock the classroom door.

She said the children knew exactly what to do from their many active shooter drills.

“They’ve been practicing for this day for years,” the teacher told NBC. “They knew this wasn’t a drill. We knew we had to be quiet or else we were going to give ourselves away.”

The loud cries of injured children soon followed the sound of gunshots from down the hall, she said and a few of her own students began to cry, fearing for their own lives.

The teacher, who was sitting on the floor in the middle of the room, motioned for her teary-eyed students to come sit with her. She held them in her arms and whispered for them to pray silently.

She tried to remain calm and silently motion to her class full of frightened students that they all would be OK.

After roughly 35 agonizing minutes police officers approached the windows of the classroom from outside the building and smashed the glass.

The students lined up and their teacher helped each one exit the building through 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.”

Later in the day, parents of her students texted her: “Thank you for keeping my baby safe.”

“But it’s not just their baby,” the teacher said, sobbing, to a NBC reporter on her front porch. “That’s my baby, too. They are not my students. They are my children.”