"It's National Walkout Day, I'm the only one from my school out here," he said in a video he tweeted. “I’m just going to be chilling here for the next 15 minutes.”
According to CNN, about 700 students attend Wilson Preparatory Academy. Blackman was the only student to leave class. He spent 17 minutes outside, one for every person who died at Stoneman Douglas High School last month, and then walked back to his Spanish class.
The school declined to comment on the issue, but told CNN Blackman is an "independent thinker."
Powerful images from the National School Walkout
Powerful images from the National School Walkout
Stop sending us to school to die #Enough #NationalWalkoutDay https://t.co/R8txeyiVvz
Elementary school walkout in Alexandria, Virginia. More than 65 kids, and they are totally silent. Look at those fa… https://t.co/JG9X38iSoE
Success Academy Hell's Kitchen elementary students doing a small walkout with a teacher https://t.co/VNuh6Zbc8t
We stand with students. #ENOUGH #NationalSchoolWalkout #ProtectOurKids #StopGunViolence @WomensMarchY https://t.co/5ZByYpmUuu
Student walkout at #LaGuardiaHighschool #NBCNews https://t.co/WXa1AbKXba
HAPPENING NOW: Hundreds of students at Eleanor Roosevelt High leave class as part of the National Walkout. They cha… https://t.co/0bSLhyfKSO
Elizabett Baez, senior at Urban Assembly Gateway School https://t.co/F5IshUZOsi
At Baltimore Polytechnic Institute, students are pouring out the back doors and making their way to the football fi… https://t.co/BSfTWoyCa5
East Lansing High School Students walking out of classes join in the National School Walkout. #ELHS #MSU… https://t.co/dAU6olHa7H
HAPPENING NOW: It’s after 10 and the walkout at Heritage High is beginning now. https://t.co/2SV4sT0fZk
Students @IamCPS SCPA #walkout https://t.co/OlkKzp6lgw
Proud to stand outside Ft. Hamilton HS today as students walk out to protest gun violence and the horrific NRA. Fea… https://t.co/410SR2xDSU
Walk out is underway at East Chapel Hill High School https://t.co/ksTpiZPjwA
Hundreds of middle & high school students in Hartford walk out of class to protest school & gun violence https://t.co/S4XcRqyiVF
RIGHT NOW: Hundreds of students protest gun violence in front of the White House, as part of nationwide walkout. https://t.co/vhKGxcjiq8
Students participating in the #NationalWalkoutDay at City High Middle School in Grand Rapids. @WOODTV https://t.co/t0RqcUjceY
Students at Wolfson H.S. walking out of class in protest for stricter gun laws. #NationalWalkoutDay @ActionNewsJax… https://t.co/LNxgIHuISm
Students at Columbia High School will ha e a moment of silence for the victims of the Parkland shooting… https://t.co/IFRBuUqdoq
#NationalWalkoutDay marching right now! A lot of us wearing orange and orange bracelets to represent the movement!… https://t.co/LdYJJ2E9j7
Massive stream of kids marching out of Williamsburg Prep to protest gun violence #neveragain https://t.co/bHKTWOWkW4
@BrearleyNYC students participating in #NationalWalkoutDay https://t.co/JWaKKuwzvM
While Congress sits on its hands, students like my son will stand and walk out of school this morning to demand act… https://t.co/ayIm1fYYI1
So very proud of our students today. Respectful, powerful, strong. Their silence was deafening. 700 strong.… https://t.co/JngotcxfsX
.@realDonaldTrump-Take a look out your window & you can see students taking part in a #NationalWalkoutDay. Or watch… https://t.co/CiIB3RN4FL
we are here and we will not be silenced #enoughisenough #nationalwalkoutday https://t.co/d5vJ4IfQPW
Currently at the White House.
Students at Warwick High School walking out of class right now. Principal expecting around 600 or more. #13NewsNow… https://t.co/hLM5B8a4iI
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He didn't think that anyone would care. “There’s going to be like six people watching this hopefully," he said in the video.
Instead, Blackman received an outpouring of support from people around the country.
Lindsay Knauf, who's from Newtown, Connecticut, where the Sandy Hook school shooting occurred in 2012, thanked Blackman for standing up.
"Seeing the action that is finally taking place means the world to all of us here," she tweeted at him.
I'm from Newtown (Sandy Hook) and seeing the action that is finally taking place means the world to all of us here. Sending all our strength to you who are forcing law makers to sit up and take notice finally.
Filmmaker and A Wrinkle In Time director Ava DuVernay retweeted Blackman's video with a Martin Luther King Jr. quote: "The ultimate measure of a man is not where he stands in moments of comfort and convenience, but where he stands at times of challenge and controversy."
"The ultimate measure of a man is not where he stands in moments of comfort and convenience, but where he stands at times of challenge and controversy ." - Dr. Martin Luther King, Jr. #NationalWalkoutDayhttps://t.co/sBtJ0II6YG