The Chattanooga Police Department made the announcement on Twitter just after 6:50 p.m. Central time.
"Our hearts and prayers go out to the family," the department added.
The child, who is now the sixth victim of the crash, has not been identified at this time.
The other five victims have been identified by family members as Zyanna Harris, 10; D'Myunn Brown, 6; Cordayja Jones, 9; Zyaira Mateen, 6; and Zoie Nash, 9.
The child's death comes after the National Transportation Safety Board (NTSB) announced the road where the bus crashed was not part of the designated route.
Honorable Christopher Hart, chairman of the NTSB, said they've also looked into the history of Talley Road, which isn't far from the children's school Woodmore Elementary.
Over the past three years, Talley Road has not had any fatal crashes. There were 9 crashes involving injuries and 43 involving property damage.
Hart also said that road was not a designated road for the school bus's route. The actual route is not known at this time, and it's unclear why the driver went that way.
So far in the investigation, NTSB says they have begun downloading video footage from inside the bus, but they had trouble due to the vehicle's damage. An expert is being brought in to help finish downloading the data.
A mechanical inspection of the bus is also underway and almost complete. Investigators are looking at every aspect of the vehicle's mechanics to see if any there were any problems that could have caused the crash.
An interior inspection will be completed of the bus as well, and an example of what the NTSB is looking for is to determine if seat or lap belts would have made a difference.
Chairman Hart reiterated the police department and noted the driver's toxicology test, which tested for alcohol and common drugs, came back clean and negative. However, samples are also being sent to an NTSB lab to test for a longer, wider range of drugs.
Durham School Services is also being investigated. They're the company that contracts out buses and drivers to school systems. NTSB said Durham is cooperating extensively and providing any and all necessary items for the investigation.
Chairman Hart said while the company has a large number of accidents, they also have 13,000 buses and thousands of drivers. The issue is not how many accidents occur but the rate of those accidents.
The Chattanooga Police Department also held a briefing earlier Wednesday, saying the investigation into the crash is ongoing and remains in the early stages.
Police said interviews are still being conducted in the case, and they haven't started talking to children at this time.
They have spoken to most witnesses, but not all of them, and said no one has confirmed reports of the driver saying "Y'all ready to die?" before the crash. They ask anyone with any further information, or anyone who witnessed the crash, to reach out to the department.
As for the driver, Johnthony Walker, no drugs or alcohol were found in his system.
"We received toxicology reports back today from the Tennessee Bureau of Investigation that shows no trace of alcohol or drugs in the driver's system. The driver was also involved in a minor wreck in September, investigated by this agency. That is also part of this investigation," said Sgt. Austin Garrett.
Authorities also reiterated that several children remain hospitalized and their conditions will not be released out of respect for the families' privacy.
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