Outside the high school's back-to-school night a few hours after the shooting, students said they had been aware that tensions were bubbling up.
"It's been three days in a row. There was a fight at McDonald's [at Broad and Hunting Park] on Friday. Yesterday, there was a fight at 15th and Pike," said one sophomore who asked that the Daily News withhold her name.
Students said that although some of the beefing teens go to their high school, they generally feel safe.
"A lot of students here, we try to stop each other from fighting," the sophomore said, adding that school officials and teachers have been keeping an eye on tensions among students.
"I feel like they have control this year," she said. "They know where to focus. The teachers have posts outside school to stop the fights."
Another sophomore stopped as she was leaving the school with her grandmother and said that "everyone" from the school was talking about the shooting Wednesday on Twitter.
The grandmother, Cynthia Stocker, said: "I'm very concerned, because too much of this is happening with these young people. Every time my granddaughter walks out the door, I'm scared. It's getting worse and worse."
Courtney Collins-Shapiro, an executive with Mastery Charter Schools, told the Inquirer that officials at Gratz recently instituted an escort program to ensure students' safety.
"There have been a lot of rumors and tension in the neighborhood for the last week, and we've been on high alert at the school," Collins-Shapiro said.
Immediately after the shooting, Philadelphia and SEPTA cops chased a group of people out of the subway station, SEPTA Police Chief Thomas Nestel said. Nestel said that one teen boy was taken into police custody from a house on nearby Carlisle Street, but that he was not suspected of being the shooter and was only being questioned.
SEPTA said southbound service was disrupted for about 80 minutes.
Contact Morgan Zalot at firstname.lastname@example.org or 215-854-5928. Follow her on Twitter @morganzalot.