The incident, some of which was recorded by a cell phone camera, happened last Thursday at the Race-Vine station in Center City Philadelphia.
According to SEPTA Police Chief Thomas Nestel III, seven of the teens were arrested Thursday morning as police descended on Ben Franklin High School in Spring Garden.
The 18-year-old, who surrendered Thursday night, is also a student there.
The 11th suspect for the Race/Vine assault/robbery has surrendered to Transit Police Detectives. All suspects are now in custody.— Thomas J. Nestel III (@TNestel3) March 24, 2017
One was arrested at the Franklin Learning Center, while another was caught after a foot chase in North Philadelphia.
All of the suspects are now facing felony charges of aggravated assault and the robbery of cell phones and iPads.
"Groupthink is overwhelming good upbringing and common decency," said Nestel. "We've had parents in there, parents of the now-defendants, who were outraged that their children were involved in such activity."
Police say most of the incidents on SEPTA occur during school dismissal time, from 3 p.m. to 7 p.m.
"The problem we're having now is that school dismissal time is becoming a period for youth violence," said Nestel. "We have kids causing pain and fear among other kids."
Nestel said there will soon be a SEPTA police officer riding every subway and elevated line during the hours after school is dismissed.
"A lot of fights occur, actually they start at school, and everything kind of flows into the subway station or flows into a car," said SEPTA Police Lt. Timothy Catto.
He says hot spots tend to be around transfer stations like 15th and Market near City Hall or busy hubs like 46th and Market, where the night before, a group of girls set another girl's hair on fire.
Six teenage girls have been arrested in this case, and all are under 16 years old.
In an interview earlier this week, a victim told Action News last Thursday's brawl broke out as he and his friends were trying to stop a group of boys from throwing ice at people.
"We were just blindsided by it, we couldn't really do anything," he said. "They had my friend on the ground, like 10 on him, so I had to step in and do what I could."
Lt. Catto tells us when police are on the train, "you're always just looking down the platform to make sure there's no problems, and to see if people are fleeing a train car. You can just tell where the problems are occurring."
"I don't like the fact that we need it, but it's necessary, that's all I pretty much have to say about it," said Lateefah Shakir of North Philadelphia.
Passengers welcome the extra patrol.
"It's just a start. I think it's more than just police being on trains. They're just reacting to the incidents that are about to happen. I think it starts in the schools and it starts at home," said Darryl Archie of Mt. Airy.