The San Antonio school district is investigating whether one of its officers used excessive force on a 12-year-old girl.
Video posted on YouTube shows the officer struggling with the girl, then taking her to the ground.
It happened at a middle school last week. A district spokeswoman said the officer intervened when two girls got into an argument.
The girl restrained by the officer was not seriously hurt, but her mother is very upset.
"You could just hear where she hits the ground. And it's nothing but concrete, cement," Gloria Valdez said. "She wasn't moving. She wasn't moving. She was just knocked out. I wanted answers and nobody could give me answers."
The officer is on paid administrative leave.
The girl's family is considering whether to take legal action against the school.