It happened at 46th and Market just before 8:00 a.m. Friday as the students were getting off the El.
According to witnesses, it stemmed from a fight between dozens of students from Boys Latin Charter School and West Catholic High.
Police believe the West Catholic student was the slasher, wounding the six from the charter school with a pocket knife. He may be facing criminal charges.
The student, who was released from police headquarters later Friday, claims the fight was an aberration. Police say it started because somebody's girlfriend got slapped earlier this week.
"They attacked us and we had to defense ourselves," the teen, Tyree, said. "It was nothing major, though."
A witness said trouble had been brewing for days.
"In the last week there have been three free-for-all fights going on. Right here, on this spot," said street vendor Brian Pugh, who watched it all go down. "We had about five to six fights going on at one time."
"There have been some issues all week, and it culminated today with a large fight," said Lt. Ray Evers of the Philadelphia Police.
The five victims from the charter school were taken to the hospital by their dean, Action News has learned.
The victims were 17 and 18 years old.
Boys Latin is a 4-year-old charter school at 56th and Cedar. West Catholic is at 46th and Market, near the scene of the fight. Police say it appears the Boys Latin students jumped off the train 10 blocks early to engage in the battle.
Boys Latin officials say they knew trouble had been brewing and rode SEPTA with those students on Friday morning. However, one group slipped off early and trouble ensued.
"Nobody can forgive them for getting off the EL. We can't defend that," said school CEO David Hardy. "But, we know that even though they got off, they didn't deserve to be stabbed."
"None of us go through this trial and error of teaching adolescents to have this kind of behavior. We're shocked and we're disappointed," said Father Timothy Ahern of West Catholic.
The investigation into this incident continues as police work to sort out the details.