B’Ellana Duquesne, center, leads the cast of “Charm.” (Stan Barouh)

Proper etiquette hardly seems the most pressing concern for the students in Mama Darlin’s raucous classroom. Several of them identify themselves as transgender; some are gay, homeless or autistic. And they all lead complicated, troubled lives.

Never mind all that, declares B’Ellana Duquesne’s Mama in Philip Dawkins’s worthily eye-opening if ultimately formulaic comedy-drama, “Charm.” No burden can’t be lightened, she insists, with an application of good manners. And if that perspective sounds naive, well, just you wait and see how quickly Mama can bring grace and enlightenment to the most reluctant of charm-school inductees.

Director Natsu Onoda Power, staging the piece for Mosaic Theater Company at the Atlas Performing Arts Center, faces some formidable challenges in putting on the best “Charm” possible. Her leading lady, Duquesne, a transgender actress who notes in her bio that she was born John Eng Jr., is appealingly unaffected; she effortlessly confers on Mama an essential sense of comfort in her own skin. But her demonstrable lack of technique is a problem: Duquesne’s stiffness weakens Mama’s authority and therefore the illusion that she has the power to transform the resistant community-center students who take her class.

If you’ve seen a movie like “Dangerous Minds,” or, going further back, “Up the Down Staircase,” you’re acquainted with the premise of hostile-pupils-vs.-the-newbie-at-the-chalkboard. Still, among the actors playing the students — costumed with streetwise style by Frank Labovitz — all are praiseworthy and two are downright sensational: Nyla Rose, as an angry transgender prostitute craving extra maternal attention from Mama, and Justin Weaks, fresh from his portrayal of a dissenting associate pastor in Theater J’s “The Christians.” In the tradition of actors who are unrecognizable from role to role, Weaks becomes an entirely new human being as Jonelle, whose complex sexual identity he embodies with an astonishing physical and psychological dexterity.

Dawkins, who wrote “Charm” after observing such a classroom in Chicago, takes some unfortunate shortcuts in the plotting; he doesn’t adequately establish, for example, why these uninterested students even bother to enroll in Mama’s course in the first place. The success of the conceit depends heavily on the moral force of Mama’s personality, and what stake there is for her in spreading the gospel of Emily Post (who materializes for an awkward fantasy sequence). Mama’s exchan­ges with the program’s director, persuasively played by Kimberly Gilbert, are useful here, but they could benefit by providing more context for Mama’s own pain.

Justin Weaks as Jonelle and Samy El-Noury as Logan, with members of the ensemble. (Stan Barouh)

The exposure, though, to the suffering of Mama’s students is handled well by Power and the cast; there are moving moments when seemingly reluctant parti­cipants such as Clayton Pelham Jr.’s Beta, a gang member, and Jade Jones’s Victoria, a homeless mother, let down their defenses and reveal the depths of their desperation.

It’s important to note, too, that “Charm” performs a vital service not only in bringing to light tales of people who live on the social margins, but also in that Mosaic employs here no less than three transgender actors, and a total of seven actors of color. Not everything has to be about tallying the victories of diversity. But few companies in town are as committed as this one is to showing the range of talent that exists in all parts of the city. This extends to the contributions of “Charm’s” other cast members, Louis E. Davis, Samy El-Noury and Joe Brack.

As “Charm” instructs, theater can at times be a potent Mama Darlin’, showing us how we might behave better toward each other.

Charm by Philip Dawkins. Directed by Natsu Onoda Power. Set, Daniel Conway and Matthew Buttrey; lighting, Max Doolittle; costumes, Frank Labovitz; sound, Roc Lee. About 2 hours 10 minutes. Tickets, $20-$60. Through Jan. 29 at Atlas Performing Arts Center, 1333 H St. NE. Call 202-399-7993, Ext. 2, or visit mosaictheater.org .