RANCHO SANTA FE, Calif. — For his 12th birthday recently, Tennessee Cumming received a gift that no other kid in the world can claim.

After a two-day certification dive in the waters off Fiji on May 16 and 17, the Rancho Santa Fe sixth-grader became the world’s youngest Junior Master Scuba Diver. It’s the highest achievement a young diver can earn from the international Professional Association of Diving Instructors, known as PADI. The achievement required hundreds of hours of training and more than 50 open-water dives.

To celebrate his new title, Tennessee (who goes by the nickname “T”) was honored recently by his classmates at The Winston School in Del Mar, which serves children with learning challenges.

T has attention deficit hyperactivity disorder, dyslexia, oppositional defiant disorder, pervasive development disorder and a processing disorder. For most of his life, school was something T hated so much, he refused to go half of the time. But since he found what his mother, Allison, calls an “island of confidence” in diving 18 months ago, he now loves getting up in the morning for school, where he earns all A’s and B’s.

“Diving has given him something he’s better at than anyone else. Kids regard him as a dive aficionado, so he’s more confident and happier, and he’s got more self-esteem,” said Allison, who with her husband, David Cumming, has three adopted children with special needs. Case, 13, has dyslexia, ADD and learning processing disorders, and daughter Samara, 8, has dyslexia, ADD and behavioral issues.

The family moved to Rancho Santa Fe from Park City, Utah, in 2014 to find schools better adapted to their children’s special needs. The move also brought the family closer to the ocean, where T could begin regular scuba training, a hobby he discovered on a family vacation in Bora Bora when he was 8 years old.

“I think I liked that I could breathe underwater for a long time,” T said. “I got to see a bunch of stuff I normally don’t see, and I liked it.”

Allison said that during that Thanksgiving week trip in 2012, T took several introductory “Bubblemaker” classes, and after each dive he returned with the words “best day of my life!”

“We’d never heard him say anything like that before,” she said. “Other than building Legos with his brother, there was nothing else he seemed to like to do.”

David Cumming, who works in the hospitality industry, said T has had a lifelong fascination with sea creatures. For his trip to Fiji, T brought along his favorite stuffed animal, a plush squid. Diving was something T wanted to pursue with earnest ever since Bora Bora, so when the family moved to San Diego two years ago, he enthusiastically dove head-first into the sport.

He was already a skilled skier in Park City and had tried numerous activities over the years, but David said his son always grew bored after a while. It wasn’t until he started diving training with PADI instructor and “Diving Nanny” Elizabeth “Bethy” Driscoll in San Diego that he found a passion that never died.

Driscoll has been diving with T almost twice a week since 2014 and has accompanied the family on several diving-related vacations. She said that since they first met, she sensed something special about T’s interest in the sport.

“I realized that he was asking the same kinds of questions that I asked in my classes,” Driscoll said. “We would start talking about diving on underwater wrecks, and we’d start laughing and get more excited about it … we just both enjoy being under the water.”

Driscoll said with all the classroom and diving time she spent with T, they started setting goals.

The hardest to reach was becoming the youngest Junior Master Scuba Diver, a category open to youths ages 12 to 15. Besides the 50 dives, the achievement requires multiple certifications, including rescue diver, emergency first responder diver and advanced open water diver.

He also had to complete training in five specialty areas. Driscoll said T picked some of the most technical and complicated specialties, including emergency oxygen provider equipment specialist, dry suit diver and peak performance buoyancy. Only the poor diving conditions off San Diego’s coast due to El Nino-related tides this year kept him from earning more, she said.

The soonest T could earn the Junior Master Scuba Diver title was his 12th birthday on May 16, so the whole family and Driscoll traveled to Fiji’s Rainbow Reef where he could pass the final steps last week. The last test, on May 17, was rescuing an “unconscious” diver (Allison played the part) from a depth of 30 feet.

With his new certification, T is now qualified for deeper and more challenging dives. He said he loves diving on shipwrecks, where over the years he’s found “sunken treasure” including an antique coin, a pocket knife, a GoPro camera and a small boat anchor. His next goal is to dive in the Tennessee River, where he wants to explore the wreck of a Civil War-era steamboat.

“Every dive,” T said, “is a treasure-hunt dive.”