Ansan, South Korea (CNN) -- First days back at school are usually filled with optimism about what's ahead, but many students at Danwon High School near Seoul, South Korea, are looking back in mourning.
On Thursday, a series of hearses made a slow crawl toward the school in the city of Ansan. Inside each, a person in the passenger seat held a portrait of the teenager they lost when a ferry capsized April 16.
About two-thirds of the 476 passengers on the Sewol ferry were Danwon students on a field trip.
Buses with blacked-out windows followed the hearses.
The school was not the vehicles' final stop. They continued on to funerals. Danwon lost a large part of a grade. Several teachers also died in the disaster.
The only students at school Thursday were those in their final year. About 100 psychiatrists and support staff from across South Korea were on hand to counsel them. Some teens arrived in hoods or wore caps to cover their faces as they made their way past journalists.
A shrine of flowers and hundreds of notes to the dead decorated the school's entrance.
"Big brother, you have to live, you have to come back," read one note.
"I want to see you," another read. "I love you and pray for you."
Many of the messages from other students expressed regret at not being able to help their classmates on the ferry traveling from the port city of Incheon to Jeju, a southern resort island.
Thousands of yellow ribbons were tied to the school gates, trees and posts. The ribbons have become a symbol of hope that survivors might still be found in the submerged ferry vessel, picking up a practice used in the United States for soldiers and hostages overseas.
Mental health care professionals will be available to the students for at least two months, said Dr. Kim Hyun-sook, head of the community mental health program in the region.
"Koreans, when they experience trauma, they feel anger and sadness but they tend to bottle it up," he said. "We're trying to encourage emotional communication to let those feelings out."
A need to heal goes beyond the school.
"I feel my heart is being ripped up," said Ryu Chang-ryul, who has lived near the school for nine years. "For three days I haven't eaten. It all hurts too much."
Kim Young-sook runs a small restaurant near the school. She dressed in black and wept as she spoke with CNN, explaining that students are regular customers.
She played a video of a 17-year-old boy she said was like a son to her.
"He used to call me auntie," she said. "He was sitting here playing guitar talking about just how important this trip was to him. I feel so bad that I could not be there. All of us, we could have done something."
An investigation into why the ferry sank is under way.
Authorities have arrested the captain and other crew members. The number of crew members charged in connection to the ferry sinking has risen to 14, said Yang Joong-jin, the chief prosecutor in the city of Mokpo. Of the 29 crew members on the ship, 20 survived. The nine others are dead or missing.
A South Korean lawmaker said Thursday that renovations last year expanded the top floor of the Sewol to make room for 117 more passengers.
Investigators want to know if the modifications made the ferry more likely to capsize.
Kim Yong-rok, an opposition lawmaker who represents Jindo, an island near where the ship sank, told CNN that the modifications raised the ferry's center of gravity. CNN asked South Korean prosecutors about that but they were unable to confirm it.
For friends gripped by intense sadness, all they can do is write messages to the dead. Many have expressed regret that they were unable to save their classmates.
"Sorry for not being there," one note said, "when you needed us."
CNN's Andrew Stevens reported from Ansan, South Korea; Jethro Mullen reported from Hong Kong and Ashley Fantz wrote this story in Atlanta.