Hundreds of students at Collingswood High School joined a nationwide protest Thursday and walked out of class for 21 minutes of silence — one minute for each of the 19 students and two teachers killed by a gunman in Uvalde, Texas.

Members of the Social Justice Club helped plan the hastily organized demonstration against school violence. As word quickly spread, school officials offered their support, and even donated a bullhorn.

At the end of the third lunch period, students began pouring from the building and gathering on athletic fields. Some sat on bleachers, while others stood on a track. A few held signs that read, “Protect kids, not guns” and “Stop killing our kids.”

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”Thoughts and prayers isn’t enough,” said junior class president Aidan DiMarco, one of the organizers. “We need background checks. We need gun control. Our politicians aren’t listening to us. But they’re going to hear us today.”

Students around the country answered a call to action to show support for students, faculty, staff, and families coping with the massacre Tuesday at Robb Elementary in Uvalde. Many are expressing demands for tougher gun laws.

In Camden, students at the high school complex, which includes four public high schools, walked out shortly after city officials held a news conference to announce plans to deploy police officers to every school in the city until the end of the school year and during summer school.

Camden County Police Chief Gabriel Rodriguez said gun crimes and firearms pose a public health emergency in the city of about 70,000. In addition to police officers, the increased patrols at 30 traditional public, charter, and Renaissance schools that enroll about 15,000 students will be staffed by the Camden County Sheriff’s Office.

In a memo to teachers, Collingswood High principal Michael Ostroff encouraged them ”to support student voice in this tense environment around gun control and school safety.” To minimize disruption of learning, he asked teachers to escort students to the demonstration. Students could opt to remain in their classrooms.

“There are so many kids who are involved and want to make a change,” said history teacher Eric Fieldman, an adviser to the Social Justice Club. “That’s exactly what student voices are supposed to do. I’m so proud of them.”

Meanwhile, at the Gloucester County Institute of Technology in Sewell, Justin Green, 17, a junior, walked out of school alone after a few classmates backed out of a planned demonstration because they feared possible disciplinary action. He looked behind him and Alyssa Peacock, 17, also a junior, was following him to the front of the main office at the sprawling campus.

“Even if no one walked out with me, I would have done it by myself,” said Green, of Deptford. “This thing is a lot more than just me.”

The two students stood solemnly for 20 minutes in front of a flagpole with their heads bowed and their hands clasped behind their backs. A few passersby gave curious stares but kept walking.

“It’s a very important issue for someone to care. Twenty minutes out of class is nothing compared to the lifetime that these parents will be without their kids,” Green said. “Those kids at the elementary school don’t have any time left.”