Tysheem Griffin was one of the fastest high school sprinters in Suffolk County but struggled with disabilities that made it hard to keep pace in the classroom.

Now the former Amityville Memorial High School standout faces life after graduation and another big race, perhaps his biggest so far, representing Team USA in the Olympic Games for disabled athletes in Rio de Janeiro in September.

Griffin, 17, who was born with Waardenburg syndrome, a rare group of genetic conditions that took most of his hearing by the time he was a toddler, will run the 400-meter dash. He qualified for the U.S. Paralympic Track & Field Team with a 50.15-second run at national trials in North Carolina on July 1. At the Paralympic Games, to be held Sept. 7-18 after the Olympics, he will compete in the T20 class, reserved for athletes with an intellectual impairment.

“I can’t believe I did this,” Griffin said in an interview last week, adding he was thrilled with the selection. “God helped me and I worked hard.”

It been a year of transition for Griffin, who ran with his high school team and with the Rolling Thunder Special Needs Program. He set a school record in the 60-meter dash last winter, won the 100-, 200- and 400-meter events and anchored the winning 400 relay team at Section XI Division Championships last spring, then graduated from high school this summer. Graduation meant leaving a school and a team that has embraced him.

“All the things I expected him to do, he accomplished,” his high school coach, Reynolds Hawkins, said. “How he performed, how he took charge — he made it contagious on the team.”

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Leaving the place he loved stung, Griffin said.

“I didn’t want to cry,” he said. “We worked together and we pushed ourselves together.”

But he’s looking forward to studying carpentry at Wilson Tech in the fall, and to flying to San Diego in August for a month of training with the Paralympic team.

“I’ve got to get used to being by myself,” Griffin said. “It’s on me now. I’m getting to be a man.”

Cathy Sellers, the high performance director for U.S. Paralympics Track & Field, said that Griffin could expect a rigorous month of workouts and strategizing. The program seeks to eke out every possible legal advantage, down to analysis of an athlete’s blood to determine if changes to nutrition are in order.

The team is currently the third best in the world, trailing China and Russia, which faces a possible ban for doping allegations, and U.S. officials want better results at this year’s games. “We hope to change that paradigm,” Sellers said.

Griffin, who ran a personal best 49.2 in the 400 this year at division championships, is currently ranked 10th in the world in the T20 class.

He will compete in Rio before a crowd expected to top 35,000, larger than any he has seen before. To win a medal, he will probably have to run a few tenths of a second faster than he has run in his life, Sellers said. “Do I think he’s capable of doing it? Yes, I do,” she said.