Some huddled in small groups, comforting each other through their tears and clutching pillows they had brought for the long journey ahead. Others were angry and defiant, shouting their demands for gun reform as they boarded the buses.

But as a vanguard of about 100 students from Marjory Stoneman Douglas high school prepared to take their fast-growing #NeverAgain campaign from their shattered campus straight to the doorstep of Florida’s legislators in Tallahassee, their message was simple: end school shootings.

Many who arrived in Tallahassee late on Tuesday night had come straight from the funerals of their friends to begin the eight-hour, 450-mile trek.

Barely an hour before, they had said their final goodbyes to classmates Carmen Schentrup, 16, and three 14-year-olds, Cara Loughran, Gina Montalto and Peter Wang, who were among the 14 children and three adult teachers murdered in last week’s shooting.

“This is how we’re coping, this is how we’re grieving, this is what is holding us together,” Sofie Whitney, a Stoneman Douglas senior, told the Guardian before boarding her bus. The teenagers will meet with lawmakers Wednesday morning to discuss gun control measures, then join a coalition of activist groups for a lunchtime anti-gun rally on the steps of the state capitol.

Whitney said the students’ attempts to channel their unfathomable grief into a focused campaign had been an exhaustive emotional whirlwind.

“The only way to get through is by making the change. There’s a hundred kids from a school that got shot up less than a week ago coming specifically to them, so if those legislators aren’t receptive that’s pretty embarrassing for them.”

Play Video 2:43 'How about we stop blaming the victims?': Florida shooting survivors speak at anti-gun rally – video

Whitney, one of the three founders of the #NeverAgain movement that on Sunday announced a nationwide March for Our Lives on 24 March, said the students were simply seeking “common sense” solutions to gun control.

“We don’t need a full bill to be written overnight but we need some action, we need them to begin helping us make the change,” she said.

Among the students’ demands are tighter background checks for gun ownership and regulations that would prevent assault weapons falling into the hands of the mentally ill.

In an interview with CNN on Tuesday, Kimberly and James Snead, a Florida couple who took in shooter Nikolas Cruz after his mother died, revealed the disturbed 19-year-old who had acquired his rifle legally, was “days away from getting counselling”.

As the fleet of buses was setting off from Parkland, thousands of students from neighbouring schools were walking out of lessons and staging impromptu rallies in solidarity. Hundreds from West Boca Raton high school left classes with their backpacks to walk the 12 miles to Stoneman Douglas.

I don’t want Nick’s life to be in vain and I’m using his life as a catalyst for a change in America, for our gun laws Lorenzo Prado, Stoneman Douglas student

Meanwhile, the #NeverAgain campaign received the backing of several celebrities including the actor George Clooney and his wife Amal, who pledged $500,000 to support next month’s march. Also, Oprah Winfrey and Steven Spielberg both announced they would match the Clooneys’ donation.

The Stoneman Douglas students heading for Tallahassee said they could feel the groundswell of support behind them.

“It feel empowering, knowing that our movement is so strong and that celebrities are backing us up,” said 11th grader Lorenzo Prado, who lost one of his best friends and the school’s swim team captain, Nicholas Dworet, 17, in the shooting.

“It’s not just people who were affected. Hollywood, New York’s talking about it. It shows how big our movement is and how impactful it can be.

Facebook Twitter Pinterest Students from West Boca high school students arrive at Marjory Stoneman Douglas after walking out in protest. Photograph: Joe Raedle/Getty Images

“It hurts to lose Nick. I knew him since 7th grade, we talked every day at swim practice. Tomorrow it’s his celebration of life, I spoke to his parents and said I wished I could be there, but I feel this would be better. I don’t want Nick’s life to be in vain and I’m using his life as a catalyst for a change in America, for our gun laws, and to make sure nothing like this happens again.”

The students have a packed schedule on Wednesday, with trip organiser Jaclyn Corin meeting with the Florida governor, Rick Scott, and others taking part in a series of roundtable meetings with state senators and representatives through the morning.

“We’re splitting into groups to divide and conquer and talk to as many as we can,” said Kaylyn Pipitone, 20, who graduated from Stoneman Douglas two years ago but joined the trip to support her friends. “We’re going to be seen and we’re going to be heard.”

Florida shooting survivors are fighting back. Here's what they need to know about gun control Read more

For the survivors and their families in the Parkland community, the slow process of healing was continuing. More funerals, vigils and memorial services were taking place, including a visit to a local church on Tuesday night of Crystal Miller, a survivor of the 1999 Columbine high school shooting and an advocate for gun reform.

On Wednesday night, hundreds of Parkland students and their families, representatives of law enforcement, and politicians including Florida’s two senators, Marco Rubio and Bill Nelson, will take part in a televised debate on gun control hosted by CNN at the BB&T arena in Sunrise.

Stoneman Douglas students have blasted Rubio in particular for accepting money from the National Rifle Association and for refusing to support gun reform measures in Washington.