At three city schools, students staged "die-ins" on Friday to protest police brutality and racism.

The Masterman die-in happened in a first-floor hallway, when roughly 100 students sat or laid down silently at mid-morning. Some held "Black Lives Matter" signs. Others closed their eyes or stared straight ahead.

The die-in lasted four minutes - symbolizing the four and a half hours Michael Brown lay dead on the ground in Ferguson, Mo., students said. They said they were deeply affected by the deaths of Brown and of Eric Garner in Staten Island. Both died at the hands of police who controversially faced no criminal penalty for the deaths.

Senior Ty Parks closed his eyes during the Masterman protest. Parks, 17, one of the organizers of the event, was emotional, he said.

"I was thinking of Mike Brown," he said.

"I was thinking of people that I know," said Amijah Townsend, 18, another organizer.

"We want to make a collective and unified statement as Philadelphia public school students," said Jamie Gobreski, another Masterman senior and protest organizer.

It was not the first action at Masterman, where students also skipped saying the Pledge of Allegiance one day.

"We're not pledging allegiance to this broken, corrupt and racist system," Gobreski said.

At Science Leadership Academy, which along with Central High also saw die-ins on Friday, senior Jasir Massey-Campbell said the protest was significant.

"But it's way bigger than just this protest," said Massey-Campbell. "I was laying there and thinking, 'That could have been me, dead.' And not only can something happen to you because of your skin color, but people can get away with it."

Students from more district schools are expected to stage an action next week outside Philadelphia School District headquarters.

And later on Friday, Philadelphia Federation of Teachers President Jerry Jordan will address the matter at a news conference.

"The decision not to indict either officer has had a tremendous, negative impact on the young people of this city," Jordan said in a statement. "A lot of change needs to happen, and as educators, we want to be part of that change."