Under a dreary sky the color of uncertainty, on a city block pocked by abandonment, a door opens and a girl of 15 steps out. With a black-and-blue book bag slung across her back, she starts walking to school, a high school sophomore of this country.

Her name is Janay Truitt, and she lives on the crime-rich and money-poor north side of St. Louis. She shares an apartment above a dry-cleaning store with two grandparents, two sisters, a brother and her mother, who leaves at 4:30 in the morning to drive a school bus. Her father lives elsewhere.

Janay sets out at 7:05 today for a city school system in which poverty, politics and mismanagement so closely conspire against the likes of her that the state recently decided to take it over. But who knows what that takeover means for this lanky girl with braids, now lugging gym clothes, math homework and a world history textbook the size and weight of a slate slab you’d find along a footpath.

Wearing a thin blue sweatshirt over a T-shirt that says “Purrfect,” she moves through the St. Louis gloom, past the dry cleaners’ trellised gates of security, past an alley where no child should play, past buildings that are well kept and buildings that are vacant, their window frames like empty eye sockets.

A man in an old green Volvo passing by beeps his horn. He is Travis L. Brown Sr., the principal of her high school, Beaumont. He grew up near here, one of 10 children. Enforcer and guardian, he drives the streets before the morning bell to signal that school matters, that he cares. I’ve been there and now I’m here, his actions say.

Janay continues on, aware that she must pass through the school’s metal detector before the 7:20 bell or else be marked again as absent, and be subjected again to a Mr. Brown lecture. She is not a morning person, does not even eat breakfast, but she has a plan for her life that begins with a first-period literature class.

She thinks as she walks. She thinks about keeping her grades up; she had five A’s and two B’s last marking period, and those two B’s, in world literature and biology, vex her.

She thinks about learning long ago how to toss balls into a milk crate nailed to a post, and about starting as a guard on the girls’ varsity basketball team this fall. When asked whether she’s a point guard or a shooting guard, she does not hesitate to answer: “Both.”

She thinks, she hopes, that with her high grades and honed basketball skills, she might one day attend the University of North Carolina, or Duke, or Tennessee. That one day she can become an anesthesiologist and make a lot of money.

“I’m thinking, probably, about trying to get out of the neighborhood,” Janay says later, explaining that at the moment she has to walk a mile to buy a decent ice cream cone, and take two buses and a light-rail train to see a movie.

She walks under a liquor store’s red-and-white beer sign and stops in front of the Upper Room Fire Christian Assembly to meet two other Beaumont students: LuCretia Scott, who wants to be a fashion designer, and Dominique Taylor, who says she might become a psychiatrist because she gives good advice.

It is 7:11, nine minutes until the bell. They push on toward Beaumont.

Beaumont High School, built in the 1920s, looms over the troubled neighborhood like a castle of trapdoors and passageways. With high student turnover and a low graduation rate, it reflects an urban system plagued by poverty and homelessness. Nearly 80 percent of the school’s 1,200 students receive free or discounted lunches.

Still, Beaumont tries. Mr. Brown, the principal, and his top assistant, Pamela Hendricks, walk the grounds so much — cajoling, disciplining, and, when necessary, hugging — that they wear sneakers with their suits. If he sees a boy wearing a hood, he shouts the school slogan, “Not at Beaumont!” If she sees a girl dawdling, she bellows, “Hurry up! Come on! What’s the problem?”

Mr. Brown says he emphasizes the possible by celebrating every success: school T-shirts one day, pizza the next. The students know that achieving a perfect average of 4.0 means they and their parents will be taken by limousine to lunch in a restaurant. The limo is a donated service, and the restaurant, of course, is several miles from here.

“You look for ways to keep the students engaged,” says Mr. Brown, enthusiastic still after 10 years at Beaumont.

Janay and her two friends rush across Vandeventer Avenue and follow a concrete path around the building, opting not to cut across the school’s wet grass. They make it to the metal detector just as the maternal Ms. Hendricks is calling, “You have 30 seconds! Everybody needs to be in class!”

A dozen hours from now, Janay will travel to a nice gymnasium in a nice suburb to practice with other young women on a traveling team called the St. Louis Queens. She will demonstrate her crossover dribble and her sweet jump shot. An accidental hit to the mouth will bloody her lip and chip a tooth; it does not stop her from playing in a scrimmage.

But that is later. For now, she settles into a small classroom in a challenged high school in the flawed school system of St. Louis, looking forward to sixth period, her favorite class, the history of the world.