Kalamazoo County Prosecutor Jeff Fink made the announcement Thursday, saying the woman was acting in self-defense.
A company hired to handle student transportation and the district said the employee was fired after the Oct. 10 incident.
Fink said a review found witnesses reported that the child threatened the employee and put a coat over her head. Fink said the child had a history of behavioral issues on the bus that officials were trying to handle.
The video was taken by a student and posted online.
Police investigated the incident as well as the ex-employee's claim that the boy had threatened her.