The trio, all students of class X, allegedly raped the girl when she was going to her school's washroom, they said.
The accused gagged her mouth with a cloth and took turns to rape her, they said.
A case has been registered against the juveniles who have been taken into custody.
A team of doctors examined the girl today, police said, adding the offence was committed on August 17, but the parents of the victim reported the matter yesterday.