Among the suspects are six youths who are said to have abused and raped the girl on several occasions last year, as well as a teacher and other students who failed to report the abuse.
The six boys, aged between 15 and 16, were part of a "notorious" clique and are accused of having gang raped the girl in the school's medical room in May.
The youths graduated from the school in autumn and were charged with rape shortly afterwards. The girl had been too afraid to say anything until she moved to a new school and confided in one of the staff there, saying that she had been abused on several occasions.
Hansjörg Bacher, spokesman for the Graz prosecutor, confirmed a report in the Kleine Zeitung that a female teacher from the school had been questioned as part of the investigation and said that she is believed to have known that the girl was being harassed by the boys and that she even heard her screaming as she was being raped but didn't do anything to stop it.
Some of the victim's schoolmates are also accused of knowing about the abuse and even witnessing the rape and failing to help her.
Local media reports that 14 days before the gang rape in the medical room the girl was being harassed by the group of boys in the toilets and screamed for help. Her classmates told their teacher, who failed to do anything and instead told the girl off when she arrived late for class.
The Kleine Zeitung reports that later that day the girl was raped in the classroom, with two boys guarding the door in case anyone tried to come in.