Martha Rivera Alanis, 33, captured the tense moments on her cell phone camera and then uploaded the video to YouTube.
In the video, Rivera Alanis can be heard encouraging the children to lie on the floor and has them sing a song from the children's TV show "Barney and Friends." The song talks about the sky raining candy.
"No, my love, nothing is going to happen, just put your little face on the floor," Rivera Alanis is heard telling one worried little girl.
Then, loud bursts of gunfire break out on the video, what local paramedics later confirmed was the sound of gunmen killing five people at a taxi stand about a block from the school.
Rivera Alanis' quick thinking earned her an honor from the state's governor. He awarded her a certificate for her "outstanding civic courage."
Rivera Alanis proudly held up the framed certificate outside the office of Gov. Rodrigo Medina de la Cruz and said she wasn't concerned with fame - only the safety of her 5- and 6-year-old students. "Of course, I was afraid, but I tell you, my kids get me through it," she said following the private ceremony.
The Associated Press contributed to this story.