Of the approximately 700 students at Wilson Preparatory Academy in Wilson, North Carolina, 16-year-old Justin was in a company of one during the national school walkout.
For 17 minutes, he said he stood by himself. He said he was disappointed no one joined him.
Earlier in the morning, the teen spoke with classmates about the walkout, but they didn't seem to know about it, he said.
Undeterred, when the time came, he stepped out by himself.
"I'm walking out for the national walk out," he said he told his teacher. "And he just let me go."
Shortly after, the teen uploaded a video on Twitter.
"Umm... hello Twitter, there's going to be like six people watching this hopefully," he says in the video.
"It's National Walkout Day, I'm the only one from my school out here."
When the 17 minutes were up, Justin went back inside, hoping he wouldn't get in trouble.
He didn't -- and said someone from the school even congratulated him.
"Now, I truly know that one person is all it takes," he says, reflecting on the experience. "No matter the age, skin color, gender—it doesn't matter."
Justin's mother, Megan, said she was shocked no one else joined in, but she wasn't surprised her son participated.
"Justin is very opinionated," she told CNN. "He's not a follower. Strong minded."
Contacted by CNN, the school wouldn't comment on the walkout.
"We teach our students to be independent thinkers," Janet Conner-Knox, who handles public relations for Wilson Preparatory Academy, told CNN. "[Blackman] is an independent thinker."