As a 6-foot-7 senior, Jefferson has matured into the Clippers' leader. The forward averaged 12 points and nine rebounds last season and helped Chester extend its winning streak to 58 games and capture a second straight PIAA Class AAAA state title.
He has smooth ballhandling skills and is dynamic in the way he attacks the basket.
This summer, Jefferson made the U.S. under-17 team but was held out of the World Championships because of an injured shoulder.
In September, he committed to Arizona, and last month, he signed his letter of intent.
"I'm at a lot of peace right now," Jefferson said. "That was the ultimate best decision.
Along with being the area's top basketball talent, Jefferson is a fixture in the Chester community. He volunteers after school as a mentor at the Boys & Girls Club before heading to evening basketball practice.
Chester coach Larry Yarbray is the center's executive director, and Jefferson said he has gone there his entire life.
"I just like helping out, being around young people," Jefferson said. "Doing things people did for us when we were kids, stuff guys like my grandpop did."
Along with mentoring, Jefferson helps clean up and vacuum the floors.
"Oh, and I play ping-pong, too," he said.
Last season, Jefferson's older brother, Temple forward Rahlir Hollis-Jefferson, added "Hollis" to his jersey nameplate. Jefferson plans to do the same at Arizona as a tribute to his mother's side of the family.
"It's for all the people in our family that love him," Hollis said. "I have eight brothers, and we're all proud of who he is."
Hollis, 59, is a lifelong Chester resident. It's not as bad a place as people make it out to be, he said. To survive, he told his grandchildren, they should pick their friends wisely.
"The kid sitting next to you in school could be selling drugs in a few years," said Hollis, who works as a painter. "And you don't need that."
Along with being Jefferson's biggest fan, Hollis can be his grandson's biggest critic, Jefferson said. After a game, Jefferson knows what to expect when he arrives at the family's modest brick rowhome on Kerlin Street.
"He's the first one to say something about how I missed three free throws," Jefferson said.
During his sophomore season, Jefferson lost his starting role with the Clippers when Yarbray benched him for a poor attitude. The coach thought Jefferson was taking for granted his chance to play varsity basketball at a young age.
Yarbray said he was certain Jefferson would mature, because of Jefferson's competitiveness as a youth in the city's Biddy League.
"You take that, and you know when he evolved into a sports figure, he was going to transcend into something special," Yarbray said.
With a strict set of rules, Hollis instilled in his grandchildren a set of manners. He ordered them to speak clearly, to say "yes" and "no." Hollis often told them that to get respect, you give respect.
As a teenager, Jefferson strove to not be labeled as a follower. When others wore their pants below their waist, Jefferson pulled his high, Hollis said.
"I want people to follow after me," Jefferson said. "I want to be a leader, and I want to set a good example. I just want to start something new."
Contact Matt Breen at firstname.lastname@example.org or @matt_breen on Twitter.