That might be because it was only three months ago that the school in Parkland, Fla., was similarly terrorized.

Kaitlyn Jesionowski, a survivor of that shooting, in which 17 people were killed, first saw news of the Friday attack on Twitter on what was the last day of school for seniors at Marjory Stoneman Douglas. For Ms. Jesionowski, it all came rushing back: the fear, the anxiety, the stress. “I started replaying what happened to us in my head, over and over.”

Nikolas Cruz, who has confessed to the Parkland shooting, opened fire in her Holocaust class on the afternoon of Valentine’s Day, killing two students and injuring four others, she said. “This has been so hard because all the emotions come back,” she said, adding that she was rushing home from school to be with her family.

Samantha Grady, 17, a Parkland classmate who was grazed in the back, learned about the Texas school shooting in a group chat during her study hall period. She stared at the phone. “It’s surreal for me, I can only imagine what they are feeling, the fear they experienced having gone through the same thing,” she said. “Honestly, I am flabbergasted.”

Dakota Shrader, a student at Santa Fe High School, was stunned, too.

“Honestly, I just had the thought in my head that somebody was going to come up behind me and hurt me, shoot me, kill me. I’m still jumpy from it,” Ms. Shrader, 16, said in an interview. “I don’t know who to trust anymore, at all.”

“This should be our safe place,” she added.

Many of the students who survived the Parkland shooting agreed.

“WE SHOULD NOT HAVE THIS IN COMMON,” Liz Stout, a senior at the school, said on Twitter, linking to a video of Ms. Shrader.