Two video clips show a year eight student being punched on the back of the head, pushed into a window and then kicked on the shin.
The Post understands the girl who attacked her, who is also believed to be 12-years-old, has been temporarily excluded from school.
But the victim's mother said her daughter was now scared to return to school, and she has reported the incident to Preston Police.
"I want more to be done," she said. "My daughter is scared to go to school. This was attack cowardly and it has left my daughter very upset. So we have reported it to police.”
The girl said she was standing on the bus station concourse after getting off her school bus when she was punched from behind by the other girl.
"I didn't do anything to her, she just saw me and started hitting me," she said.
"She has got in trouble for it and been sent home from school. But she is allowed back tomorrow and my friends say she has threatened to do it again.
"I can't understand why she has done this."
The girl says this is the second time she has been the victim of an unprovoked attack out of school in the past three months. In the other incident, in December, an older girl from another school wrestled her to the floor and "stood on my head."
The Post knows the identity of the victim but has chosen not to name her.
"That's why we have reported it to the police,” she said. “I'm frightened."
The Post contacted the school where he two girls are pupils and we were told: "This happened outside school and it was reported to the police, so any comment will have to come from them."
The spokesperson refused to say if the girl accused of the latest attack had been suspended.
A spokesman for Lancashire Police said: "We have had a report of an assault and we are looking into it."