Nilaja Sun could have caved to expectation. As a teaching artist in drama, she could have arrived at a tough Bronx high school armed with A Raisin in the Sun. The kids have heard of it; it’s what they anticipate. She could have brought Romeo and Juliet, whose protagonists are young if not gifted and black. But this brave young artist chose Timberlake Wertenbaker’s thematically apt Our Country’s Good, in which 18th-century English convicts transported to Australia put on a production of George Farquhar’s Restoration comedy The Recruiting Officer and thereby learn the transformative power of art. Sun has guts — though to judge by the undulating, elastic physicality with which she invests the 16 characters of No Child . . ., the one-woman show based on her experience in the arts-education trenches, few bones.

No Child . . ., which is being presented by the American Repertory Theatre (at the Loeb Drama Center through December 23), was commissioned by New York’s Epic Theatre Center, where it premiered last year before settling in Off Broadway and winning 2007 Obie, Lucille Lortel, Outer Critics Circle, and Theater World Awards. Funny, troubling, and humane, the 75-minute tour de force takes its name from the Bush Administration’s No Child Left Behind legislation, which, with its emphasis on standardized testing, in Sun’s estimation leaves lots behind. Don’t worry, she’s there to pick it up, arriving for her six-week stint at the show’s fictional Malcolm X High School a ball of sunny energy radiating the news that “from now on we are nothing but thespians, which means actor, citizen, lover of all things great.” “Lesbians?” retorts one tenth-grade wit. When Sun introduces Timberlake Wertenbaker’s script, another exclaims, “Yo, Justin Timberlake done wrote himself a play?” The teaching artist has her work cut out for her.

So does the solo performer, a gifted actor, mimic, and master of accents whose Malcolm X High houses eight distinct razzing, jiving, smart-ass students, their overwhelmed first-time teacher (who doesn’t last the six weeks), a well-meaning if dictatorial principal, a put-upon, Jamaican-accented keeper of the metal detector, several barking replacement faculty, and Sun herself, according to the bent and venerable African-American janitor who serves as narrator “something they ain’t never seen before.” Yet she’s no more a rarity than he, who refuses to let even his demise get in the way of his duties. Having watched the building and the system fall apart for 50 years, this custodial Chorus finally pushes his broom across the River Styx. But that doesn’t stop his turning right back around to keep us abreast of things, his “new friend, Arthur Miller,” having assured him that there is no reason “a dead man can’t make a fine narrator.”

Under Hal Brooks’s concise direction, Sun is all over the ugly-linoleumed, water-damaged place, carrying on multi-way conversations in which each of her band of students is immediately identifiable: drama queen Shondrika, with her jutting hip and smoldering attitude; wild, gesticulating Brian; anxious José, always yanking at his shirt; cocky Jerome, arms hanging, legs spread, a slouching potentate in a plastic chair. When Sun almost throws in the towel, it is Jerome who persuades her to take it up again — by quoting from Our Country’s Good to the effect that “theater is an expression of civilization.”

Sun doesn’t offer a 10-point plan for rescuing our crumbling, demoralized, prison-like urban public schools (though clearly NCLB isn’t doing it for her). What touches her — and through her us — is that beneath the jaded aura of delinquency issuing from these teens is an eagerness to learn, to expand, to open themselves to new experience and be changed by it. The writer/performer does not peer through rose-colored glasses at her profane, antsy, lip-giving thespians (or their inadequate teachers). Some fall into the old traps or through the cracks. Not everyone makes it to Our Country’s Good, what with such interference as unsupportive parents and a gang slaying. That the show goes up at all is a miracle — if not necessarily the big one these kids need. But Sun, a diminutive dervish of a performer talented enough to surmount the stereotypical aspects of her script, paints a picture that’s both satiric and poignant — even if it only limns the elephant in the room.

Another one-man throng is on stage at the Lyric Stage Company of Boston, where an engaging Neil A. Casey is performing a solo re-enactment of the classic 1946 Frank Capra film It’s a Wonderful Life (through December 22). Steve Murray’s adaptation, called This Wonderful Life, may be short on personnel, but it does allow its single performer to re-create and send up the hoky if beloved film about a guy saved from suicide on Christmas Eve by a guardian angel who demonstrates how important — and connected — his life has been.