Derrick Kelson was sitting downstairs playing a video game several weeks ago -- a week after learning how to give CPR -- when one of his brothers ran to tell him his youngest brother, Trevon Boyd, wasn't breathing.
Derrick, a sophomore at Bluffton High School, sprinted upstairs and found his mother already on the phone with 911. But she was crying and was too upset to follow the operator's directions.
Trevon's eyes were wide open, but he showed no other signs of life.
Then, Derrick took over.
When Derrick, 15, received his schedule at the beginning of this school year, he didn't want to be in his sports medicine class, according to his mother, Vanessa Kelson.
That changed after a few sessions.
Derrick often came home wanting to show his family how to tape ankles or ice and elevate injuries. But the favorite thing he learned was CPR.
"I thought it was cool to learn and practice in class," Derrick said. "But the first thing that came to my mind was that I'm not going to need this."
The sports medicine class, an elective, first began at Bluffton High School in 2007, teacher and athletic trainer Todd Stewart said.
"I always wanted to teach a class like this," he said. "Everything you learn in the class is something you can use."
Since the class was first offered, it has grown to include a series of five different courses and has become a health science major in the school's Career and Technology Education department, according to department chairwoman Libby Ferrato.
Stewart said the sports medicine and health science courses have become popular -- about 125 students go through the two sports-medicine classes each year.
The classes are hands-on, Ferrato said, and teach students a variety of skills that can be helpful at home, school and work.
"For kids to pick this up, we think, 'Wow, what class and skill is more important than teaching students how to save someone's health and life?' " Bluffton High athletics director Dave Adams said.
"If I were to ask Derrick or his family what was the most valuable class he has taken, it's obvious which one he'll say."
One one-thousand, two one-thousand, three one-thousand ...
After counting to 10, Derrick's younger brother still was not breathing.
So Derrick gave him two breaths and started chest compressions.
One, two, three, four, five ... twenty-six, twenty-seven, twenty-eight, twenty-nine, thirty.
Even though less than a minute had passed, it seemed he had been waiting an eternity for 6-year-old Trevon to respond.
Although the operator walked Derrick through the steps for CPR, he said he knew exactly what he was doing.
What he couldn't have done without was the training that prepared him for that moment.
"I knew what I was doing and I knew I had it down, but there was a lot going through my head, and I was really scared because it was my brother," Derrick said. "But I don't think I would have been able to do the CPR without the class."
Stewart said Derrick responded exactly the way students are taught. Many people don't act because they don't want to do something wrong or they wait for someone else to step in, Stewart said.
"Derrick threw all that out the window and did what he was trained to do," Stewart said. "He really did a great job stepping up and took control of the situation."
When Trevon, a first-grader at Red Cedar Elementary School, still wasn't breathing after the first cycle of CPR, Derrick started another.
Check for breathing, two breaths, 30 compressions.
Only then did Trevon's chest start to move.
He was breathing on his own again.
Shortly after Derrick resuscitated his brother, the paramedics arrived.
Trevon had suffered a seizure. He was taken to Hilton Head Hospital, then to Memorial University Medical Center in Savannah, where he remained in intensive care for three days.
"The doctors said it was a really good thing I knew how to do CPR, because I could have been a big part in saving his life," Derrick said.
Though the cause of the seizure is not known, Trevon has had several appointments, and doctors continue to run tests, Vanessa Kelson said.
She said she is proud of Derrick and glad the school offers the class.
Derrick thinks everyone should take the course. After all, he's seen its benefits firsthand.
The Beaufort County School District took a step in that direction last year, when it required all coaches at all schools -- whether paid or volunteer -- to be certified in CPR.
"The safer the community, the better for everyone in that community," district chief student services officer Gregory McCord said.
Because of what he learned in class and the incident with his brother, Derrick is considering a career as a coach and a sports trainer.
For now, though, his mother is grateful for the skills he learned.
"I am just so thankful that they have that class there," Vanessa Kelson said. "... (It's) not just for a grade or a credit, but it can actually help out in the world, and it saved his brother's life."
Follow reporter Sarah Bowman on Twitter at twitter.com/IPBG_Sarah.