Columbus City Schools Wednesday began the process of firing Laura Roberson, 59, for the Tuesday incident, The Columbus Dispatch reported.
The school district said Roberson assaulted a 9-year-old special-needs student on her bus while driving the girl home from school.
The student's foster mother reported the incident to police Tuesday evening.
The incident was recorded by the bus video-surveillance system, district spokesman Jeff Warner said.
"We could see that she absolutely was physically inappropriate," Warner said of the driver. "We don't know exactly what precipitated it."
Roberson was notified Wednesday that she was fired without pay pending a district hearing on Tuesday on a charge of malfeasance, Warner said.
Warner said the district moved quickly because of comments by Superintendent Gene Harris last week that she wasn't happy her staff failed to act quickly enough against another driver accused of misconduct.
In that case, driver Brenda Abdul-Mateen had been the subject of a number of complaints dating to 2010, including running stop signs while a student was being sexually assaulted on her bus, then disregarding the student's assertion that she was raped. Abdul-Mateen was also accused of threatening a female passenger and her family with violence and holding a grade-school boy while girls beat him.
Abdul-Mateen resigned last month after the district finally decided to fire her.