Cell phone video shows the teacher picking up the boy and slamming him into a countertop as other students attempt to intervene.
The boy's mom said he had tried to retrieve his backpack from the teacher before the altercation.
"School staff responded immediately to intervene, de-escalate the situation, and ensure the safety of those involved," Principal Dr. Amber Grady wrote in a note to parents Thursday following Eyewitness News' request for comment Wednesday evening.
The Fort Bend County Sheriff's Office confirmed it's conducting an active investigation and is reviewing the video, but declined to comment about possible charges.
Fort Bend ISD said the substitute teacher will not return to work at the school district.
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