In 1999, they were American suburban teenagers. They were hanging out in the cafeteria, chatting with the basketball coach, dreaming up after-school plans to go fishing.

None of these survivors likely imagined the remote possibility that gunfire and explosive devices would rip through Columbine High School that April 20, setting off 49 minutes of horror that still echo through their lives.

Less than two weeks after the Columbine massacre killed 13 people and wounded more than 20 others, 8,000 demonstrators in Denver marched for stricter gun control.

Nearly two decades later, Americans are still marching.

A National School Walkout begins Friday, coinciding with the 19th anniversary of Columbine, and coming in the wake of February's mass shooting that killed 17 people at Marjory Stoneman Douglas High School in Parkland, Fla.

Columbine is no longer among the 10 deadliest mass shootings in modern U.S. history.

Former students who survived the tragedy tell CBC News that whatever they thought might come after Columbine, they could have hardly envisioned going through lockdown drills with their own kids.

Here are the stories of four survivors, in their own words.

KRISTI PETRIE, 35

Kristi Petrie, centre, from a Columbine High School photo. Petrie was a junior when the shooting began. 'I just finished lunch. Our alarm went off. We started seeing and hearing kids running out the door. We could hear things, some of the gunshots. I couldn’t even put myself in my parents’ shoes at the time, but now it’s even more terrifying.' (Kristie Petri)

Nineteen years ago, we felt we were an anomaly. This was not something that would happen again.

I don't know now that we felt this sense of responsibility to change anything. But Parkland definitely mirrored Columbine for me. It made me stop and think: "Holy shit, it's been 19 years and we're watching the exact same thing play out."

There was one thing that stuck out with me in counselling. They said, "You guys are going to work through this, figure it out, go on with your lives. But don't be surprised if this pops up when you have children, and you have to send your children to school." That stuck with me.

Petrie today with her children. (Kristi Petrie)

I have a daughter, two-and-a-half years old, and a 10-month-old. My two-and-a-half year-old is in school. And you hear after each of these shootings, that parents say that for some reason, they got extra time with their child that morning, before losing them.

And there's mornings when my daughter is extra affectionate, extra sweet, or we have this sort of really sweet moment, it terrifies me.

I would tell the Parkland students: Have patience with yourself, with however the healing process manifests itself.

There's going to be fear. Things will knock them down. Take care of themselves, be graceful and allow themselves to feel the things they feel and don't try to force any healing. It has to happen its own way.

AMY OVER, 36

Amy Over was a high-school senior when two gunmen killed 12 students and a teacher at Columbine. 'I was walking down for lunch and started hearing some commotion. We looked outside the window and I thought it was a fight. My basketball coach Dave Sanders must have been working the lunch shift. He told us someone was outside shooting and we needed to get away from the windows. He saved our lives.' (Amy Over)

The first day I dropped my daughter off at preschool, I collapsed in the parking lot. I thought it was a heart attack. The doctor asked if I ever had a panic attack. Could any trigger have caused this? I said I just dropped my daughter off at school, and I'm a Columbine survivor.

I've worked hard on my trauma. I'm in a place where I want to share my story because I own my story.

I ran as fast as I could underneath a table. I could hear bombs going off and screams. When the gunmen started coming in to shoot is when I ran. We ran out that front entrance door and we were being shot at as we ran.

Over, second from left, with her family in Colorado. (Amy Over)

My daughter will be 13 in September. Now we're into lockout and lockdown drills. She knows these safety procedures are here because of Columbine.

We didn't know how to handle this back in the day. We didn't have the social media platforms. These Parkland kids are amazing. This is how they're coping right now. The Mama Bear in me wants to know, are they taking care of themselves. Have you guys eaten?

I'm getting a pen pal this week from Parkland through the Rebels Project [a support group run by Columbine survivors].

I hope they ask me what their heart desires. I hope we build a friendship, a support system. I hope they feel love and support, and know they're not alone, that they can call me and their feelings are validated.

AUSTIN EUBANKS, 36

Austin Eubanks, in a high-school photo, was wounded in the shooting. 'My best friend was killed right in front of me. I was shot twice. It was just a few minutes after we entered the library, and a teacher ran through the doors, yelling for everybody to get under the table. The perpetrators entered the library and went pretty methodically from section to section, coming to ours last.' (Austin Eubanks)

We were living in a time when this was not normal. My best friend and I had just been talking about whether we'd go fishing or play golf after school, which were kind of the big decisions of the day.

It was only a matter of weeks until I was in active addiction. I was prescribed opiates and a couple other medications intended to medicate me after the profound tragedy I'd just endured.

But I finally found the courage to do whatever it took, and I stayed in treatment for 14 consecutive months to resolve the underlying trauma, the survivor's guilt, and to live a life that wasn't controlled by substances.

When I heard about Parkland, I was in Colorado School District 51, on a stage speaking to students about empowerment.

I walked offstage and picked up my phone. I had a text message from the local ABC affiliate that just said, "Can we talk about what's happening in Florida?" And I just knew. I wrote back, "How bad is it?"

Eubanks was addicted to opioids for years after he was wounded at Columbine. The father of two boys is now clean and works as a keynote speaker about substance abuse. (Austin Eubanks)

This one hit especially close to home once I turned on the news and actually saw what was occurring. The imagery that was coming out. The armoured vehicle up on the grass, the barrage of police cars, the students running out of the school with their hands above their heads.

Knowing that almost two decades have passed between those two tragedies, and yet the imagery being so similar, the predominant emotion is anger.

I talked to some of the students. After a tragedy like this, there's a tendency to withdraw or detach emotion whenever emotion is difficult.

People find a way to medicate. I chose substances.

And I talked a lot about being careful not to get so fully consumed with activism that you detach from your own healing, because you can medicate with activism and lose a sense of normalcy that a kid in their junior and senior year of high school should have.

MICHELLE PORTER, 36

Michelle Porter, here at 18, was a Columbine senior. 'I was eating lunch and it was kind of a ruckus coming from outside. People were yelling, "Get down!" I ran upstairs to where the classrooms were. We could hear bombs going off for a while.' (Michelle Porter)

They said the same thing about arming teachers 19 years ago, and my friends and I laughed. We loved our teachers and thought they were wonderful, but it was laughable to think of them having weapons.

We choose them to educate people, to protect them in certain ways, but not to have to kill for them.

The Parkland students are saying, enough is enough. More guns is not safer. There's something deeper going on here, to have this reaction. There's mental health involved, but the access to the weapons is allowing this to continue.

I teach bilingual kindergarten now. We have our fire drills, our active lockdown, our soft lockdown, a hard lockdown. And I tell them it's in case something dangerous is in the school. We have to practise if something scary happens.

And the kindergarteners say, "Like a dog?" And I say, 'Yup, just like a dog."

Porter now teaches bilingual kindergarten in Texas. (Michelle Porter)

I still have scars, but I don't want to lose my wounds. Because if I do, I'm not empathetic and compassionate and this experience means nothing.

That's what I want the Parkland students to hear: It's OK to have wounds because the wounds we carry with us affect who we are as people.

Sometimes they make us angry and bitter and send us down a dark path; sometimes they allow us to forgive and move to a better place.