On April 20, US students plan to walk out of class. They'll only return under one condition.

Earlier this week, a former student walked into Marjory Stoneman Douglas High School in Parkland, Florida, and killed 17 of his former classmates and teachers.

It was the 18th school shooting in the United States this year alone.

Now American high school students have had enough and they’re ready to take action.

LISTEN: Why are US gun laws unchanging, despite massacre after massacre? We discuss, on Tell Me It’s Going To Be OK.

They’re demanding their congressmen and women finally address the country’s lax gun laws. They believe they have the right to attend school safe in the knowledge they will live through the day. They want clear and definitive action and they want it now.

So on April 20, the 19th anniversary of the Columbine School Shooting, US school students are planning to walk out of school. They will take to the streets, and not return to their classrooms until Congress updates the country’s gun laws.

High school students are talking on message boards to make April 20th the day they all walk out of school and don’t come back until Congress updates the gun laws as it’s their lives on the line. Plz retweet or share for visibility as this is a great idea. #FloridaSchoolShooting

— Noah Evslin (@nevslin) February 16, 2018

Well if it comes down to it I am willing to walkout on the April 20th even if i get a suspension or detention because my life matters more than a piece of paper.#NationalSchoolWalkout

— ❄Alan Vargas RESISTS❄???? (@TheAlanvargas) February 17, 2018

if you are a hs student who is feeling as helpless as me, here is our change: we walkout of school to show the adults how scared we are & make our voices heard. we walk for gun control, we walk for the victims of any school shooting & we walk for humanity. #NationalSchoolWalkout

— kenya (@sunIightandmoon) February 17, 2018

I’ve never gotten in trouble in school before, ever. Not a detention, not a CSI, etc. yet I’m willing to tarnish my record to stand up for what I believe in. Every single school walkout that I can participate in, I will do my best to be in. #NationalSchoolWalkout

— ????VALE???? (@Vale_Elii) February 17, 2018

How sad is it we have to protest for our own safety #april20 #floridashooting

— Madi Leigh Engels (@itsmemadi97) February 17, 2018

The movement began after educational psychologist, David C. Berliner, suggested teachers should agree on the gun legislation they want and take it to Congress. If it’s not accepted, Berliner explained in a blog post, they should walk out of school.

“Our country’s legislators, and the voters who send them to make our laws, can then choose: Teachers and (most) parents for sane gun laws, or, the NRA that provides our legislators money to avoid making the laws that could reduce the carnage we see too frequently.

“Almost all of America’s three million teachers — nurturers and guardians of our youth — want sensible gun laws. They deserve that. But they have to be ready to exert the power they have by walking out of their schools if they do not get what they want.”

Berliner advised teachers to start meeting now to write model legislation and submit it to state and federal legislators.

The movement quickly gained traction and has resulted in plans for a National Walk Out Day on April 20.

LISTEN: Mia Freedman and Amelia Lester discuss the shooting at Las Vegas’ Mandalay Bay Hotel that left 59 people dead.