Many Marjory Stoneman Douglas High students carried white ribbons and white roses in memory of the victims
The Florida high school where 17 people were shot dead earlier this month has reopened.
Students at Marjory Stoneman Douglas High returned to classes for the first time since it was hit by one of America's deadliest mass shootings on 14 February.
Many of the students carried white ribbons and white roses in memory of the victims.
Since the massacre, survivors have become vocal advocates for gun law reform, leading a national boycott campaign, appearing on TV shows and organising mass street protests.
Their return to school coincided with a pledge to end the sale of assault-style rifles by a major US gun retailer.
Dick's Sporting Goods said on Wednesday that it would immediately end sales of the deadly firearms and would not sell any guns to people under 21.
Gunman Nicholas Cruz had legally purchased a gun at a Dick's store, the retailer's chairman Edward Stack said, although it was not the gun used in the massacre.
Mr Stack said the company "felt it needed to do something" and that lawmakers must act to change the current system - which he argued was unable to prevent dangerous people buying guns.
Around 50 heavily armed police officers were present at Marjory Stoneman Douglas High as students returned to classes on Wednesday.
But while law enforcement was meant to help the community feel secure, it was viewed with suspicion by some survivors of the massacre.
"This is a picture of education in fear in this country. The NRA wants more people just like this, with that exact firearm, to scare more people and sell more guns," student David Hogg, who has become a vocal campaigner for gun reform, said.
"I know one of those bullets could be shredding through me if I was misidentified as a school shooter," he added.
The first day back started at the fourth period, so students and teachers could return with the classmates and teachers they were with during the shooting.
Grief counsellors and therapy dogs were also on hand across the campus. Florida school superintendent Robert Runcie requested that media did not fly helicopters above the school, out of respect for the student's wishes.
I pray that today is the beginning of our long and difficult journey from grief, sorrow and anger to a new consciousness of hope, compassion and love. Thank you to our young people for leading the way. Welcome Back! #MSDStrong #NeverAgain pic.twitter.com/ytCNfMxwSe— Supt Runcie (@RobertwRuncie) February 28, 2018
While pupils said they were nervous to return to school without classmates, many said they had been given hope by the nationwide #NeverAgain campaign for gun control that has followed the shooting.
Students tweeted messages of support as well as calls to continue with activism as they returned to school.
"I am so proud of how the kids at my school have been fighting because we all want change to happen and, as we see the progression, it really shows us that people do care and they do hear what we have to say," 15-year-old Alexis Grogan, who wore trainers that said "MSD Strong" in reference to the school's name, said.
The freshman building where the shooting took place remained closed.