When the fourth-grader moved around again, the bus driver hit the brakes.
The incident happened Tuesday in the Ambridge Area School District, about 25 miles northwest of Pittsburgh. Police Chief Jack Lively said police will not release the driver's identity until charges are filed, likely by Monday.
Police have seized a surveillance video from the bus. The boy was knocked to the floor out of camera view, but is seen getting up holding his face. Other students are knocked around and one is flipped over a seat.
The driver and the boy have had run-ins before, parents said.
The boy's mother claimed he was "singled out" for discipline when students got rowdy in the past and asked school officials to have someone monitor the bus. Lively said the monitor was on the bus Tuesday, but didn't get out of his seat to intervene.
School officials said they are reviewing the incident.
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Information from: Beaver County Times, http://www.timesonline.com/