In a 1983 photograph by Mary Ellen Mark, two teenage runaways sit on a Seattle sidewalk. One of the two girls is bathed in piercing sunlight, her athletic socks dressed up with high-heeled sandals, a bouquet of flowers clutched in a fist like a baseball bat. She hugs her knees tight and hangs her head low, as if trying to make herself smaller. But her gaze is long, pensive.

Looking at Mark’s photographs of adolescent girls and young women — 30 of which are on view in “Girlhood” at the National Museum of Women in the Arts — you might get the sense that simply pointing a camera toward a subject gives her a certain maturity.

But girlhood is often shaped by the guise of adulthood, tried on like a costume — until it stays on for good. Girlhood is small feet wading in too-big high heels. It is a game of make-believe more real than reality. Like a vibrant dawn that succumbs to the flat expanse of day, girlhood — especially as seen in Mark’s images — is intensified by its ever-encroaching end.

Mark, a photojournalist for numerous magazines, who died in 2015, is best known for her long-term project documenting a subject known as “Tiny” — first encountered as a homeless youth and ultimately as a mother of 10. Throughout a five decade career, Mark was drawn to outsiders, to people who weren’t given the best chance at life. They felt “more human,” Mark said.

When photographing children, Mark strove to capture their precocious maturity. “I like to see them as adults,” she said. But in this show, they always seem to be — eerily, uncomfortably — both grown-ups and . . . not. A poised self-consciousness comes over them like an intermittent breeze. Their girlhood resurfaces like a flame that refuses to be snuffed out. In a photograph taken on a beach in New Jersey, two girls wear matching bikinis. Their hips seem to sway in anticipation of a dance club, still years away. Their hands, clasped at their ears, suggest children listening to bedtime stories. Their eyes appear vacant, searching.

What Mark’s work gets at is not simply the way the adult is latent in the child but how the beginnings of womanhood surface — sometimes bubbling up with that ubiquitous, inexplicable wish that children have to be seen as grown up; at other times, yanked into the light by circumstances.

Mark’s images span social class and culture, painting an image of girlhood with strong contrasts. She photographed circus performers in India, schoolchildren in Ukraine, American prom-goers.

Her rare images that could be called joyful capture girls boasting a nascent self-awareness that has yet to give way to insecurity. In one, a girl stands in the kitchen of a Bronx shelter, her arm twisted in the air with the bravado of a dancer. She takes the pose of a woman but maintains an unbridled, childlike confidence.

In Mark’s more difficult images, harsh realities intrude on girlhood. In a photo from her 1978 trip to India’s red light district, a teenage sex worker wearing schoolgirl braids and lurid makeup prepares for a night on the street. She locks eyes with the camera — in other words, with the viewer — and her hands fall open, as if grasping for something lost.

Mark’s work has always invited awkward conversations. Critics would list the types of outcasts she photographed, as if they were sights to leer at in a carnival. They praised her for going places others wouldn’t dare. During much of her career, Mark’s subject matter was certainly radical, but simply representing the marginalized is no longer seen as commendable for its own sake. We know how giving a voice to the voiceless can become patronizing; how telling their story can devolve into exploitative drama; and how a subject’s struggles can supersede their humanity.

In Mark’s photos of girls, their struggles are descriptive, not deterministic. “Laurie in the Bathtub,” for instance, is just a mysterious girl bathing. Her face hovers over soapy water; her loose bangs curl into playful horns; her hair reaches upward with the vivacity of Medusa’s snakes. It’s not until you read the description that the context becomes clear: She is in a mental institution.

Mark garnered a reputation for capturing lives vastly different from her own. But even as the photos in“Girlhood” span continents, they seem close to home.

In a 1993 interview with British Vogue, Mark described her early years as a “problem child” in a “lonely household.” Her parents left her on her own often; she lied about her age to support herself as a waitress; and the rituals of youth — pajama parties, Halloween — became a kind of coping mechanism. “When you don’t have one of those happy homes, you are into dressing up and putting yourself together,” she said.

Having taken narrative control in her own adolescent life, Mark was able to pass that control on to her subjects. In many of her photographs, the world seems to bend to the girls’ perspectives.

One photo shows a girl named Lakeisha resting on the back of chair, totally captivated by the sky. Her feet dangle, one without a shoe — as if the practical considerations of walking on the ground were suddenly irrelevant. The zigzags of cracked concrete behind her appear like her own creation. It’s as if she’s willed the Earth to lift her to the sky. Lakeisha’s small body is only a fraction of the frame, and yet at the same time, she fills it.

Mary Ellen Mark: Girlhood

National Museum of Women in the Arts, 1250 New York Ave. NW. nmwa.org.

Dates: Through Aug. 8

Admission: $10; $8 for seniors and students; free for members and children under 18. Timed-entry tickets are strongly encouraged. Face masks are required, except for children under 2 and visitors who are unable to wear a face covering due to a medical condition.