Parkland, Florida (CNN) Fred Guttenberg lost his daughter Jaime when a gunman killed 17 people at Marjory Stoneman Douglas High school two weeks ago. On Wednesday, his son went back to school.

Students and teachers returned to class on the Parkland, Florida campus, seeking normalcy after the mass shooting thrust them into the center of the national gun debate.

Guttenberg said it was bittersweet to see his son go back. "I'm not scared because this is now the safest school in America," he told CNN.

But it's still hard, he said. "My son walks in here without his sister. My daughter's friends walk in there. They used to always walk in with my daughter ... and they're walking in there without her."

Administrators hope to ease students back into a routine this week with a modified schedule of half days.

Good morning Eagles: here is today's schedule. Everyone will start in 4th Block as we RECLAIM the NEST pic.twitter.com/wxQYnemIWi — Principal Thompson (@PrincipalMSD) February 28, 2018

"It was nice to be in class, but it didn't feel like class," senior Kevin Trejo said. "It was just a gathering in a way."

The day began with 17 seconds of silence to remember those they lost.

Students described a roller coaster of emotions as they walked into a school filled with friends, grief counselors and comfort dogs. Throughout campus, posters offered encouraging messages, reminding them "We get courage from each other."

"We know things will never, ever be the same, but we're going to try to figure out how to move forward," Broward County Public Schools Superintendent Robert W. Runcie said Tuesday after classes ended.

The shooting galvanized a student-led movement calling for stricter gun laws. After two weeks of protests, funerals and vigils, students are contending with how to balance activism with SATs, advanced placement tests and applying to college.

"I think it's hitting us all hard because we have all been so involved with the movement and now we just have to be students," sophomore Tanzil Philip said.

No backpacks, and building behind emergency tape

From the start, it was clear things would be anything but normal. The campus was swarming with media, law enforcement officers and flashing patrol cars, and well-wishers passing out flowers.

"It does give me comfort to know we do have more security, but also, it makes me think back to the day," junior Sawyer Garrity said as she sat in her car, waiting in a long line of traffic to enter the school parking lot.

As classes resume, the school is trying to strike a balance between safety and creating a supportive environment, Principal Ty Thompson said. Students were told not to bring backpacks this week, as the focus will be on emotional readiness and comfort, not curriculum, he said.

Building 12, where most of the massacre occurred, remains closed off behind emergency tape with its windows covered. The absence of the building forced administrators to shuffle classes around and clubs to move to new locations.

Empty desks become memorials

For many students, it was cathartic to reunite with friends and teachers they had not seen in two weeks , senior Demetri Hoth said. Some wanted to dive straight into classes, but many more preferred to take it slowly, he said.

"Our minds aren't there yet to talk about math and statistics and science," Hoth said.

Teachers made the transition easier by asking students how they wanted to proceed, Hoth said. "I think we're still not sure yet," he said.

In his AP literature and composition class, students stood in a circle, passing lines of string among each other as they shared their feelings in a visual metaphor for coping within the community.

"The end goal was to show how we are all connected and how we can count on each other," he said.

Students decorated empty desks with flowers and mementos in honor of the victims. One desk in Trejos' AP literature class was decorated with flowers and the University of Florida Gator for Carmen Schentrup , who would have turned 17 on February 21.

'The days don't feel real anymore'

Trejos sat behind her and next to another student who was missing from class Wednesday because he's still recovering, he said. The class felt said the class felt empty, not only without her, but because of students who are still recovering from gunshot wounds.

"It was tough, she just wasn't there," he said. "The days don't feel real anymore."

Teachers passed out comforting items such as Play-Doh and coloring books, said Garrity, who received a stuffed bunny she named Quincy.

The night before, Garrity video-chatted with friends to ease their nerves. Her fellow drama club member, Isabela Barry, played her guitar. Since the shooting, Barry has had trouble sleeping in the dark. To alleviate anxiety, the two had "a virtual sleepover" Tuesday night, leaving their computer cameras on as they slept.

The girls met outside the school and walked in together with their friend Ashley Paseltiner. By the day's end, the girls said the sense of community lifted their spirits.

"We got through it together," Paseltiner said. "We've just got to keep going, remember the people that we lost and make the most of what we have here."

Today we go back to school for them. Today we have to be strong for them. I'm scared any time I leave my house, but I know we have to do this for them. We won't let him take our school. We won't let them be gone in vain. This is all for them. — Ashley #shineMSD (@ashleydrama5) February 28, 2018

'Not a single bill has been passed'

The shooting sparked nationwide debate over gun laws and mass shootings. Runcie commended the students for keeping the subject at the forefront of the conversation as they grapple with their own trauma.

"We continue to be inspired and amazed at our students and how well they responded to this, how they provided leadership on a national level to bring attention to some very salient issues that have emerged from this tragedy," he said.

Survivors and victims' families have not let the issue fade, even as the push for new regulation appears to lose momentum at federal and state levels.

"The thing that makes me the most mad is even after two weeks, even after two weeks of all of this, not a single bill has been passed in the state or federal level," student David Hogg said Wednesday. "All we have now is more guns and more chances for things to go wrong."

Discussions about how to keep the movement alive rumbled through classrooms Wednesday, English teacher Darren Levine said.

As he tried to plan the rest of the year's curriculum, conversations kept turning to marches planned for March 24.

"That's on a lot of their minds, because we don't want to let this movement die."