D.C. United’s Griffin Yow, left, drives the ball past Steve Birnbaum during a training session. (Courtesy D.C. United)

Kathy Yow peered through the black-tarped fence surrounding D.C. United’s training grounds that hot day last summer, angling to spot her son.

Inside, Griffin Yow, 15 at the time, was engaged in drills with adults who play soccer for a living, most notably with an English chap named Wayne Rooney.

“My jaw was hanging open,” she said this week. “I thought, ‘I can’t believe this is happening.’ ”

After the session, one of several to which Coach Ben Olsen invited her son and other United academy players, she started the car for the ride home to Fairfax County.

She then turned to Griffin and said, “I cannot believe you just trained with him.”

Griffin, at that time a quietly confident sophomore-to-be at Centreville High, said, “It was unbelievable, mom. This was the coolest thing ever.”

Eight months later, he is not only training regularly with Rooney; they are teammates, separated by 17 years and, oh, a few million dollars.

Two weeks ago, Yow became the 12th player — and one of the youngest — to sign a homegrown contract with United. Rooney, the captain, made a locker-room speech formally welcoming him to the team.

“I am actually a Chelsea fan,” Yow said, “but I loved watching him” with Manchester United.

Now 16½, Yow has withdrawn from public school and enrolled in an online program. He trains with the first team and plays for Loudoun United, D.C.’s new second-division squad. (On March 16, he scored the first goal in team history.)

He seems on course to make his D.C. debut in a May 22 friendly against Spain’s Real Betis or in another nonleague game this summer.

Absent a driver’s license, Griffin receives rides from his mom. While he practices, Kathy — a former North Carolina State forward who played high school and club soccer with U.S. women’s Coach Jill Ellis in Northern Virginia — runs errands or jogs around the RFK Stadium property, United’s training base until a new facility opens next year in Leesburg.

Things have moved fast in Griffin Yow’s young life. Asked whether he expected to become a pro so quickly, he said: “No way. A year ago, I was training with the first team once in a while, and I was just grateful for that. The dream was there to go pro, but I had no idea this was going to happen.”

A left-sided attacker with nimble ball skills and a killer instinct, Yow entered United’s academy about two years ago. The organization monitored him closely, and as he drew greater attention with the U.S. under-17 national team, D.C. took action to avoid losing him to an overseas offer when he turned 18.

United invited him to training camp in Florida and soon extended an offer. Terms were not disclosed.

By signing, he altered a trajectory that would have included teenage passages such as high school graduation, SATs and college visits. Major NCAA programs were aching for his talents.

“It definitely concerned us,” said his father, Sam. “My parents and my wife’s parents, they were even more concerned. The first thing out of their mouth was, ‘Go to college, go to college, go to college.’ And when they heard some of the schools interested in Griffin, they were over the moon. For sure, that was something we had to think about.”

Sam Yow said he sought counsel from people in the soccer business and parents who had been in similar situations.

Kathy Yow said: “For me, first and foremost, it was, ‘What are we doing? This is the not the pathway I envisioned. Should we really be doing this?’ The more we discussed it, it just made sense. There were so many more reasons, when we sat down with Griffin, where we said, ‘Why not? Let’s see this through and see where it takes us.’ ”

Education will not go away, however. On rides to and from practice, Griffin opens his laptop and does homework. At home in Clifton, he takes classes for three to four hours each weekday through the K12 online program. A proctor working with United’s academy remains involved, as well.

“It’s a different pathway, but he still has me to nag him,” Kathy said. “Education is still going to be a large part of his future; it’s just going to be a nontraditional way.”

Griffin seems happy with the arrangement, saying, “Missing out on college soccer and the whole college experience is big, but being out here and training with these guys every day, and also being able to still do school online, it worked out pretty perfectly.”

Socially, Kathy said, “he will still kick it around in the neighborhood with his buddies and go to the prom.”

But Griffin’s special skills — and United’s new platform for fostering development — eased the pro decision.

“In some ways, signing Griffin without Loudoun doesn’t make a lot of sense,” Olsen said. “His development is going to be sped up."

In the past, United would loan prospects to the Richmond affiliate, but as an independent team, the Kickers had their own ideas and plans. With Loudoun, D.C. supervises operations and works closely with the coaching staff. Loudoun also trains at the RFK grounds, but Yow and others on MLS contracts practice with D.C. most of the week.

Yow was a substitute in Loudoun’s season opener at Nashville and started in the second match, a 1-1 draw at Memphis in which he scored on a deflected shot from distance in the first half.

Olsen said, “I am looking forward to working with him and getting him fully integrated with the group and seeing what his ceiling is. . . . There is a lot to like and he has a bright future. I love being part of that process.”

United will not rush him. Physical maturation is part of it. “I might not grow height-wise,” said Yow, who is 5-foot-7, 135 pounds, “but I will definitely thicken out.”

Aside from Loudoun assignments, Yow is probably headed to the U-17 World Cup qualifying tournament May 1-16 in Bradenton, Fla. If successful, he and the U.S. team would compete in Brazil in the fall.

Reflecting on his rise, Yow said, “I don’t want to feel like I’ve made it already. Sometimes I have to remove myself from everyone, from the hype telling me how great I am and how great this opportunity is. This is just the start. Signing this contract is everything I worked for but also a new chapter in my life. I need to keep working, stay humble, and I think there is much more to come.”

D.C. United at Orlando City

Where: Orlando City Stadium.

When: 6:30 p.m. Sunday.

TV: FS1.

Records: United 2-0-1, 7 points; Orlando 1-1-2, 5 points.

D.C. probable starters: GK Bill Hamid; Ds Leonardo Jara, Frederic Brillant, Steve Birnbaum, Joseph Mora; MFs Paul Arriola, Russell Canouse, Junior Moreno, Luciano Acosta, Lucas Rodriguez; F Wayne Rooney.

Orlando probable starters: GK Brian Rowe: Ds Shane O’Neill, Lamine Sane, Robin Jansson; MFs Ruan, Carlos Ascues, Oriol Rosell, Sacha Kljestan, Joao Moutinho; Fs Nani, Santiago Patiño.