When the breaking news footage out of Texas splashed across the TV inside her high school office, student body president Julia Cordover had been hand-delivering goodbye cards to the staff on her last day of high school.

Just like that, all thoughts of celebrating disintegrated with a barrage of bullets 1,200 miles away.

As the mass shooting was unfolding at Santa Fe High School in Texas, students and teachers at another high school, Marjory Stoneman Douglas in Parkland, Florida, couldn't help but relive the emotions of the rampage in their school three months earlier.

"I was just in disbelief," Cordover, 18, told NBC News. "I was, like, this can't be happening again. I couldn't tell if other people were seeing what I was seeing."

Fellow senior Allyson Adak heard the news a few minutes before she took her final AP exam.

"It felt like Valentine's Day all over again, and your mind wanders off when you're supposed to be concentrating on the test," said Adak. "I started feeling anxious and I started feeling sad. I was almost about to cry.

"But I knew I wasn’t alone. My friends in the room were feeling the same way."

In teacher Jeff Foster's AP government class, what was supposed to be a celebration of the seniors last day quickly turned into a painful reminder of their own horrific experiences.

"When I was watching the news on my computer, I made the conscious decision to put it on the big screen and plug in the audio," Foster said after the Texas shooting. "Everybody stopped what they were doing and watched it.

"The students all seemed to be in disbelief and angry. Watching them, you could see, looking into the kids' eyes, you could see them remembering when they had cameras in their own faces three months ago."

Law enforcement sources said nine students and one teacher were killed at Santa Fe High School in Friday's mass shooting — the highest death toll in a school shooting since the Feb. 14 massacre at Marjory Stoneman Douglas, which left 17 students and teachers dead.

Police swarm Santa Fe High School in Texas after a shooting on Friday. Steve Gonzales / Houston Chronicle via AP

In the wake of the carnage in Parkland, a number of students launched a nationwide advocacy campaign to tackle the gun control issue and to register students to vote to take the fight directly to pro-gun politicians.

But Foster said it's going to be hard for his students to not feel shaken by the latest episode of gun violence.

"You go from saying, 'We won't let this happen ever again,' and then this happens," said Foster, whose 11-year-old and 6-year-old daughters reluctantly came to visit his school on Friday for the first time since the Feb. 14 shooting and were jarred by what they were seeing on the television news.

"What do you say now?"

Cordover said she struggled through the rest of her day, especially her last period in astronomy class — in the same room she was in when the gunfire broke out in her own school.

"Today’s my last day," she said. "We were so excited to go into today's celebrations, but this put us all in the same mood as Feb. 14. I know a bunch of us were very paranoid all day today.

"I felt it in the pit of my stomach because we still feel that pain."

On social media, several of the gun control movement's leaders expressed their outrage and sorrow:

"Santa Fe High, you didn’t deserve this," tweeted Parkland advocate Emma González. "You deserve peace all your lives, not just after a tombstone saying that is put over you. You deserve more than Thoughts and Prayers, and after supporting us by walking out we will be there to support you by raising up your voices."

Santa Fe High, you didn’t deserve this. You deserve peace all your lives, not just after a tombstone saying that is put over you. You deserve more than Thoughts and Prayers, and after supporting us by walking out we will be there to support you by raising up your voices. — Emma González (@Emma4Change) May 18, 2018

Another Parkland survivor and student leader, David Hogg, said, "Get ready for two weeks of media coverage of politicians acting like they give a s--- when in reality they just want to boost their approval ratings before midterms."

And within hours of the shooting, March for Our Lives, a group founded by the students, released a statement:

To the students and faculty of Santa Fe High School, we are with you. #MarchForOurLives pic.twitter.com/3DYXOhmwsP — March For Our Lives (@AMarch4OurLives) May 18, 2018

Foster said a meeting planned for Saturday by gun control advocates was to discuss a voter registration drive. That meeting now is expected to take a different agenda.

Some Parkland students are already making plans to offer their support to their Santa Fe counterparts perhaps even catching a flight there, said Cordover.

"We want to show the students how they can be active, how they can use voices to speak up," she said.