According to the transit agency, the incident happened after school Wednesday, around 3:30 p.m., on a train near the Erie Station.
Video of the assault shows a female student yelling at another group of students sitting on the train.
SEPTA Police Chief Thomas Nestel said the victims in the attack are Asian and the four suspects are African American females.
The altercation quickly escalates.
In the video, one of the female students, now a suspect, is seen throwing a punch. The group of victims sit and try to shield themselves.
One of the suspects gets into the face of another female student who is standing. Then the suspect's attention goes back to the students who are sitting.
More obscenities are shouted and then the situation turns more violent.
The female student who is standing gets hit in the face multiple times. Then her head is slammed against the side of the train and she is taken to the ground. She is punched and stomped on repeatedly.
One of the suspects is seen taking off her shoe and hits the victim repeatedly.
Then you hear someone's voice and the video stops.
"This was an attack based on ethnicity and ethnic slurs were used by the attackers," Nestel said.
On Thursday night, the Philadelphia District Attorney's Office approved charges of aggravated assault, ethnic intimidation, criminal conspiracy, simple assault and other related offenses against four of the juveniles.
One suspect has been charged with one additional count of robbery for an attempted theft of one of the victims' air pods.
"This matter will proceed in the juvenile justice system; as such, we will not be releasing the names of the defendants. We are grateful to our partners in law enforcement, particularly SEPTA Police, for their swift investigation of this incident," said the district attorney's office in a statement.
At this point, SEPTA police say the attack seemed unprovoked. They are now working with other city and school leaders to provide support for the victims.
According to Nestel, tips came pouring in after the video went viral. He said one of the calls came from one of the suspect's mothers.
"A mother called when she saw her daughter as one of the people involved in the assault and reported her daughter as being one of the attackers," he said.
Community Spokesperson John Chin said he has been in contact with the family of the teen who stood up to her attackers.
"The family is very distraught by the incident. They've been in meetings with the school district all day today. In fact, the family, and other families, of students in the school district have brought in legal representation," Chin said.
The students who were injured attend Central High School, Nestel said.
Officials said that starting immediately, a police escort will be present on the Broad Street Line for students returning home from Central.
Anyone with information on this incident is asked to contact SEPTA police at (215) 580-8111 or Philadelphia police at 215-686-TIPS.