The students all attended Portage High School when the alleged incidents took place.
The three teens were accused of groping and threatening female classmates on the bus.
Monday 18-year-old Joe Francisco Carnell pleaded guilty to felony charges of strangulation and intimidation.
Last Friday, 17-year-old Charles McCloud-Smith pleaded guilty to similar charges. Ashley Toney, 18, is set to go on trial in June.