Ivan Nolia, 14, leaps off the diving board last week at the Banneker Pool in Washington. (Michael Robinson Chavez/The Washington Post)

Enough already, Marcus Shedrick decided. Enough with the stiff-legged pencil jumps, the dinky cannonballs, the stuntless “psychs.” He was 12, a week away from seventh grade, no longer at the bottom of middle school hierarchy. It was high time he learned to dive.

He stood at the edge of Banneker Pool, the faded “11” beneath his feet a reminder of the water’s daunting depth. A lifeguard stood beside Marcus, rattling off instructions: Straighten your arms. Bend your knees. Lean forward. Take your time. Marcus narrowed his eyes, aligning his hands above his head and tilting, tilting, tilting until his feet left the pavement and the water swallowed him.

“It doesn’t even look like a dive. It just looks like you’re falling in,” the lifeguard said with a laugh.

“I need more practice,” Marcus said solemnly as he hauled himself out of the pool, his end-of-summer quest still out of reach.

A few feet away, the diving board loomed, a stiff barometer of youthful bravado. Childhood is full of little tests, the results suggesting what kind of person a kid might grow into, and the diving board is among the most telling — and most punishing. Its 12-foot tongue is an invitation for a few seconds of airborne glory but also for back- and belly-smacking public humiliation. There is no going back, no way to fake it. Like growing up, it’s a blind thrust forward.

One afternoon last week, a few days before the city pools began to close, Banneker Pool in the Shaw neighborhood was a churning ecosystem of youth. Tiny children toddled in the shallows, tugging at their doughy yellow life vests and rubbing sunscreened cheeks. Knobby-kneed girls did handstands and competed to see who could hold their breath the longest. Teenagers, savoring summer’s final days, fussed and flirted. The girls sunned themselves in faded lounge chairs, feigning indifference as the boys tried to coax them in.

Aava Niva, 5, walked the length of the board as if she were walking to her doom. She stood at the end, tiny toes curling, fists clenched. Her mother, Pia, treaded water and gave her the thumbs up, shouting encouragements in Finnish.

Aava had taken the swim test — a straight, solo shot across the deep end — the week before, despite her mother’s insistence that she should wait until the family returned to Finland, after summering in the District. She was stubborn; she wanted to keep up with her brothers, 11 and 14, whom she had watched enviously all season as they sprung off the aluminum board with so much force it almost touched the water below.

Barely three feet above the water’s surface, Aava squinted and huffed. She leaned forward to peer at the water below, then looked up, wide-eyed and petrified. A line was forming behind her: boys in sagging basketball shorts serving as swim trunks; shivering cross-armed girls in bright bikinis; grown men in Speedos, shifting their weight back and forth to avoid scorching their feet.

Finally, with a grimace, Aava hurled herself over the edge. She was a bundle of bony, flailing limbs, and she disappeared into the cobalt water with a tiny plunk. Her grin after she surfaced took up her entire face. Once she made it to her mother’s waiting arms, she looked expectantly at her brothers, who were tussling in the shallows, oblivious to her triumph.

In the waning sun, Tameka Brown stood rolling an unlit cigarette between her fingers. Her son Nate lumbered along the diving board over and over, corking, roundhouse-kicking and landing, always, squarely on his back with a sickening crack.

“Ohhhhhhhhhh!” a group of older boys shouted each time Nate hit the water, while the boy’s mother shook her head and laughed. She remembered how he’d thrown himself into the deep end when he was just 2, eager to follow his brothers and sisters.

“I swear, I thought he was going to die,” she recalled. “We just couldn’t keep him out.”

To be a kid is to learn most lessons the hard way or else ignore the lessons entirely.

Nate, now 13, crawled out of the water and got immediately back in line for the umpteenth time.

“That had to hurt,” Brown said.

“Nope,” Nate declared, and his mother rolled her eyes.

After hours of grinding practice — and a few dozen Fortnite videos watched during adult swim — Marcus’s moment of truth came when his father, a D.C. Department of Parks and Recreation employee, arrived and beckoned him to leave. Marcus begged for a few minutes and explained that he had spent the whole day in pursuit of one crisp, perfect dive.

“Let’s see what you got,” said his father, Robert, raising his eyebrows.

Marcus climbed the ladder. The board was warm and rough beneath his feet. He bounced a few times, then stood still. He peeked over his shoulder to make sure his dad was watching.

The long-awaited dive was relatively sharp and straight, miles away from his early face plants but still nothing like the sleek arcs of the grown-ups he’d admired. Still, Marcus emerged, sputtering and beaming. He tried to play it cool as he high-fived his dad, reining in his pride.

“Got to keep working on it,” the boy said.