"The investigation revealed relentless activities directed toward Phoebe to make it impossible for her to stay at school. The bullying for her was intolerable," Scheibel said.
Six teens -- four girls and two boys -- face charges including statutory rape, assault, violation of civil rights resulting in injury, criminal harassment, disturbance of a school assembly and stalking. Three younger girls face delinquency charges.
Scheibel said the harassment began in September. She said school officials knew about the bullying, but none will face criminal charges.
"The actions of these students were primarily conducted on school grounds during school hours and while school was in session," the prosecutor said.
Scheibel refused to discuss the circumstances of the rape charges.
Prince's family has moved away from the area and could not immediately be located for comment. Scheibel spoke for them at a news conference to announce the charges.
"The Prince family has asked that the public refrain from vigilantism in favor of allowing the judicial system an opportunity to provide a measure of justice for Phoebe," she said.
Some students accused of participating in the bullying have been disciplined by the school and will not be returning to classes.
Scheibel said the case is still under investigation, and there may be additional charges.
The Massachusetts Legislature cited Prince's death and the apparent suicide of 11-year-old Carl Walker-Hoover of Springfield last year when members passed anti-bullying legislation earlier this month.