A substitute teacher in Texas was fired and arrested Friday after a video showing her allegedly assaulting a high school sophomore was posted online, officials said.

The teacher, Tiffani Shadell Lankford, 32, was charged with aggravated assault after the incident occurred at Lehman High School in the city of Kyle, south of Austin, the Hays County Sheriff’s Office said.

It wasn’t clear what prompted the alleged assault, but a disturbing video posted by the mother of a student appeared to show Lankford repeatedly punching the sophomore, then throwing her on the ground and stomping on her head.

“There is absolutely no excuse or circumstance that can justify what you see unfold on the video,” said Tim Savoy, a spokesman for the local school district. “It is unconscionable what this adult did to one of our students.”

After the alleged assault, the district said Lankford was immediately removed from the classroom and questioned by a school resource officer.

The teacher was quickly fired and reported to the Texas Education Agency, the statement said.

The sheriff’s office said it reviewed several videos and conducted several interview before taking Lankford into custody.

Lankford had undergone training and passed a background check before she began working as a substitute in September, the district said. She worked in district classrooms 18 times since September 13, the statement said.

Lankford couldn't be reached for comment and it wasn’t immediately clear if she has a lawyer. Court records didn’t list one for her.