Saturday marks 25 years since two students fatally shot 12 classmates, a teacher, and wounded more than 20 others at Columbine High School in Littleton.

Why it matters: Although it wasn't the first, the 1999 tragedy has become a blueprint for other shooters over the last quarter-century, ushering in a new era of school gun violence that has only gotten worse.

By the numbers: So far in 2024, there have been more than 50 incidents of gunfire and nearly 20 deaths on school grounds nationwide, according to Everytown for Gun Safety, the largest gun violence prevention group in the U.S., which formed after the 2012 Sandy Hook shooting.

• Since 2013, there have been over 1,200 such shootings, killing more than 400 people. Nineteen have been in Colorado, leaving eight dead.

What they're saying: The impact of gun violence lingers "not only within a community but also within families, within the mental health of … survivors and [their] support systems," Kiki Leyba, a teacher at Columbine High School who survived the shooting, said this week during a news briefing in Washington, D.C.

• "There is something that's cellular, where our bodies remember trauma. And so for me, every year around April, around the time when everyone is celebrating the spring, my body starts to feel anxious," Kristina Hanley, another Columbine survivor, told NPR.

Yes, but: Despite more shootings and a lack of federal legislation banning assault-style weapons, survivors say hope can still be found.

• They see it in Colorado's efforts to tighten firearm regulations and the Biden administration's new rule expanding background checks for gun purchases.
• They also see it in young people, who have never known a world without mass shootings and active shooter drills.
• "They're tired of this, and they're going to show it with their votes. They'll make a difference," Leyba said.

What's next: Survivors and other community members will meet at 7:30pm Friday on the west steps of the state Capitol for a candlelight vigil.

• On Saturday, roughly 2,000 current Columbine students and staff — and people from around the world — will devote the day to service projects.