PARKLAND, FL — Survivors of the second-deadliest U.S. public school shooting were brought to tears on Wednesday by empty seats and missing friends at roll call as they returned to their Florida high school two weeks after 17 students and educators were massacred there.

Upon emerging from a half-day of classes intended to ease their return after the tragedy, some of the roughly 3,000 teens who attend Marjory Stoneman Douglas High School in Parkland, Florida, described their emotional day.

Samuel Safaite, a 15-year-old sophomore, said students in his Spanish class broke down when the teacher took attendance and read out the name of Luke Hoyer, a 15-year-old slain in the attack.

“A lot of people started crying because we all knew he was gone,” Safaite said. “It was difficult for a lot of people.”

Many of the students carried white flowers when they arrived at the school in the morning and wove through hundreds of uniformed police officers providing security for their return. Emotional-support dogs also were on hand to provide comfort.

Nikolas Cruz, 19, who had been kicked out of the school for disciplinary reasons, is accused of carrying out the rampage.

The shooting inflamed the nation’s long-running debate on gun rights as defined in the Second Amendment of the U.S. Constitution. It also sparked a youth-led gun control movement featuring survivors of the attack, who have already lobbied lawmakers in Florida’s capital Tallahassee and Washington, D.C.

“We will push for change and our children are going to be the change agents,” said Jeannine Gittens, 44, who drove to the school to be there to meet her son Jevon, a 16-year-old junior, when he arrived on the bus. “We see that things have to change and we are not going to stop until they do.”

The building where most of the victims died was closed, surrounded by a chain-link fence decorated with signs reading “MSD strong” and “Pray for Douglas.” Florida lawmakers are contemplating tearing it down and replacing it with a memorial to the victims.

As she left the school with her mother and 18-year-old brother, sophomore Marisa Lopez, 16, said some friends were talking about leaving the school.

“I don’t think that some people are ready to move on,” Lopez said, adding that some of her friends had witnessed the shooting of Scott Beigel, a 35-year-old social science teacher who was one of the three adults killed in the attack. “I just don’t know if some of them are ever going to get over it.”