The image of an empty field of chairs facing a “Class of 2021” banner became the center of a viral conversation on gun violence in America. “The Lost Class” was a powerful stunt pulled off by agency Leo Burnett for gun safety advocacy group Change the Ref.

Directed by Hungry Man's Bryan Buckley, the campaign created a fake high school in Las Vegas and invited former NRA President David Keene to speak at its commencement ceremony. To an audience of 3,044 empty seats—the number of students who wouldn’t graduate in 2021 after losing their lives to gun violence—Keene’s speech on the battle over the Second Amendment was chillingly spliced with audio of 911 calls during school shootings. There was also a petition for politicians to enforce universal background checks for gun ownership. It currently has nearly 42,000 signatures.

“Graduation day is meant to symbolize potential and achievement,” Manuel Oliver, co-founder of Change the Ref and parent of a child lost in the Parkland massacre, said in a statement. “Let’s not lose another class of students to the gun violence epidemic. Let’s demand that we make graduating America’s children more important than gaining uninhibited access to guns.”