An officer lifts a middle-school student into the air and slams her to the ground.
She lies motionless as he handcuffs her. Some students shout out; others laugh as she's escorted away.
The cell phone video, which spread rapidly after it was posted online this week, has sparked investigations by police and school officials in San Antonio, Texas, CNN affiliate WOAI/KABB reported.
"It's very concerning. It's alarming to see this," San Antonio Independent School District spokeswoman Leslie Price told WOAI/KABB. "And while we want to get all the details, I want people to know that excessive force will not be tolerated in this district."
Gloria Valdez told the CNN affiliate that her 12-year-old daughter is the girl shown in the video.
"You could just hear where she hits the ground. And it's nothing but concrete, cement," she said. "She wasn't moving. She was just knocked out. I wanted answers, and nobody could give me answers."
The officer, according to Valdez, told her "he did what he had to do at that moment."
The school district told WOAI/KABB that the officer had been placed on administrative leave pending the outcome of its investigation.
This isn't the first time school police officers have been accused of using excessive force.
Last year, a police officer working at a South Carolina school was fired after video circulated on social media showing him violently removing a student from her desk.
That video sparked widespread outrage and questions about what role police should play in schools. At the time, the officer's attorney defended him, saying his actions were justified.
Last month, the Baltimore school system's top cop and two others officers were placed on administrative leave after the release of a cell phone video showing one of the officers slapping and kicking a young man. Now the officers are facing assault charges in the case.
About 43% of all U.S. public schools -- including 63% of middle and 64% of high schools -- had school resource officers on their grounds during the 2013-2014 school year, the National Center for Education Statistics said in May.