Most of them were not yet born when students shot a dozen people to death inside Columbine High School in Colorado, an atrocity that sparked a national debate over guns exactly 19 years ago.

But on Friday, on the anniversary of the April 20, 1999, shooting, the several thousand high school students who walked out of schools across the city and beyond to rally against guns in Manhattan said they felt they lived in a world of near-constant Columbines.

The teenagers spoke angrily of active shooter drills since kindergarten, of backpack and locker searches, of mock lockdowns sitting in silence in classrooms with the lights turned out, as they gathered in protest in Washington Square Park. And they spoke of the numbing barrage of school shootings in America — by some counts more than 200 in the past two decades.

[See photos of Friday’s student walkouts in cities across the United States.]

Caroline Castellano, 16, a sophomore at Hunter College High School in Manhattan, had only just recently heard the name Columbine. “So I did the classic internet search,” she said. “It really freaked me out really quickly.” Near her, with a pink Post-it note with the word “victim” written on it on her forehead, stood Kathya Rodriguez, 16, a sophomore at the High School of Fashion Industries, a public school in Chelsea.