When they were kids, they could only watch as their friends pedaled off. In college, they saw other students go ten-speeding around campus. As grown-up Washingtonians, increasingly surrounded by bike lanes, bike commuters and bike-share stations, they have stood aside as a city zips by on two wheels.

And so, a few decades later than most, 13 adults gathered last week in Alexandria to take care of some unfinished childhood business: learning to ride a bicycle.

“D.C. has become such a bike town; it’s everywhere,” said Chris, a 29-year-old staffer at a child advocacy group in the District. He stills bears the scars of his disastrous first attempt to learn at age 7: a small one on his ankle and an enduring one on his self-esteem.

“I got my foot caught somehow and went down,” said Chris, who asked not to be identified by his last name because he doesn’t want to be known as one of the few adults who never navigated such a basic rite of passage. “Everyone knows how to ride a bike. It’s embarrassing.”

Embarrassing seems to have become unbearable for many of the area’s non-biking adults; thousands of them are fueling a boom in adult learn-to-ride classes. The Washington Area Bicyclist Association is holding 14 adult-only classes this spring and summer, including some courses that cost as little as $1o in the District, Alexandria and Arlington. The association may add more adult classes to meet the soaring demand, and other groups offer similar classes.

“As soon as we add a class, it fills up,” said Matt Liddle, who runs the outdoors education program for mid-Atlantic REI stores, where a four-hour session costs $85.

The interest has been particularly acute in Washington, where even Supreme Court justices are tooling around on bikes — and sometimes toppling off them.

On Saturday, 74-year-old Justice Stephen Breyer had shoulder replacement surgery at MedStar Georgetown University Hospital after fracturing his shoulder in a bike tumble on the Mall. It was the third time that Breyer, who is expected to make a full recovery, has been injured riding a bike.

Despite those kind of mishaps, the region’s bicycle renaissance has nudged non-riders to seek a way — ideally a low-profile way — to catch up.

“Not knowing how to ride a bike as an adult is not something you admit at a cocktail party,” Liddle said. “You don’t want to ask a friend, ‘Hey will you teach me?’ ”

Perfecting their balance

At the Sunday morning class in Alexandria, nervous novices lined up with loaner bikes along the paved yard of an elementary school. One had her helmet on backward. And yet most of them, the instructors promised, would master the basics by the end of the three-hour class. As for why it’s taken this long, instructors heard the usual laments:

For 27-year-old Josh Krantz, it was growing up in the Bronx, where stories of bike thefts and bike wrecks dissuaded his parents from getting him on a two-wheeler.

For Zainab Kamara, a 42-year-old accountant, it was being born into a non-riding family in a London neighborhood where cycling was not that common.

For many, the thing they most remember about cycling is the wipeout that ended their original attempts to learn. Decades later, the basic dread remains the same.

“Now my biggest thing is just fear of falling,” said Chris, the 29-year-old nonprofit staffer. “I’m older and bigger; if I fall I’ll break something.”

But learning to ride has actually gotten easier since he took his tumble. There will be no training wheels on these full-sized Treks, no instructors running beside, steadying their seats and shouting breathless encouragements before shoving them to their fates.

Instead, the instructors just remove the pedals.

“Okay folks, you’ve probably noticed something missing on your bicycles,” instructor Dan Hoagland said to the waiting riders.

The modern method emphasizes balance before all. Pedaling, gear-shifting and other higher-order skills can wait. With the pedals temporarily removed, students mounted up and push-glided across the playground using only their feet. With looks of fierce concentration, they kept their feet off the ground for longer and longer intervals, seeking that ineffable point of balance that allows a grown human to balance above two skinny wheels.

It was as easy as falling off a bike. Which is what Mary Jones promptly did.

“Oh oh oh oh,” said Jones, a civil servant from Alexandria nearing retirement age, as she executed a slow-motion tumble across her suddenly horizontal ride. She stood up laughing, with three instructors already at her side.

But, unlike the time four of her brothers tried to teach her on the family’s one bicycle back in the 1960s, this time Jones got right back on. She wants to learn to ride as a surprise gift to her “special friend,” a gentleman about to retire from his own government job.

“I want us to go bicycling on all these beautiful trails around here,” said Jones, pushing bravely off for another wobbly glide across the pavement.

Slowly, their tracks became straighter, their bodies more centered, their speeds something more languid than lurching. With each pass, they loosened their death grip on the handlebars and let their weight do the steering.

Student by student, instructors reattached the Shimano pedals. First just one, so the riders could get a feel for the “power stroke.” And then both, allowing astonished grown-ups to ride properly, if shakily, round and round the playground.

“It feel like a childhood dream come true,” exalted Krantz, one of the first to graduate to two pedals.

Krantz, a federal worker in Alexandria, came to a stop, planted his feet and recalled all the times in life he couldn’t do this, like the time he had to take a van back to the hotel by himself while his college buddies went for a ride in Costa Rica.

“I’ve already texted everybody, my mom, my dad, my wife,” Krantz said. “My sister told me not to text and ride.”

Tearful triumph

The instructors talk about the glow that comes over the faces of adults who finally break through, vanquishing a secret fear that has dogged them since grade school. Hoagland had a woman burst into tears the previous week at an Arlington class. Another student bought his training bike as soon the session was over.

“It’s the best part of my job,” Hoagland said.

Anthony Mansell, 25, a climate change activist who lives near U Street in Northwest Washington, grew up in a rural part of Wales where he never learned to ride.

“It’s such an oddly good feeling,” he said, beaming, as he pedaled slowly by. “It’s not been fun to dread the day someone says ‘Let’s go on a bike ride.’ ”

Mansell plans to sign up for Capital Bikeshare, which allows users to check out bicycles from stations around the region. Several students mentioned the wildly popular program (it passed 4 million rides earlier this week), as well as other spokes of the bicycle boom that has enveloped Washington in the past decade. The District has gone from three miles of dedicated bike lanes in 2001 to 56 miles today. The percentage of workers commuting by bike has tripled in that time.

“I’ve really envied people who could just jump on a bicycle and go,” said Kamara, the accountant, who was now doing just that.

When it was Chris’s turn to take off with both pedals, he took a deep breath, said “Let’s do this,” and pushed off.

And away he went, riding a bike, just like everybody else.