Sarah Steele, Star of LCT3"s "Slowgirl" AS Becky, the 17-year-old motormouth in the new Off Broadway play "Slowgirl," Sarah Steele rips through dialogue with such scatterbrained delight - "Stuff comes into my head, and I just say it, you know? I don't, like, check where it fits on the Appropriate Topics Scale or whatever." - that this actress's own poise at a recent interview was startling at first. But at 23, Ms. Steele is an old pro at exploring how troubled teenagers resort to exhibitionism to bury their vulnerabilities. Greg Pierce's "Slowgirl" is the third New York production in eight months for which Ms. Steele has drawn critical acclaim playing adolescents; she has become such a go-to actress for this type of role that she didn't have to audition for any of the three plays. She was a high school misfit last fall in Julia Brownell's "All-American," and she portrayed a range of characters this winter in Erika Sheffer's "Russian Transport": a gawky 14-year-old as well as three Russian girls who are ensnared in the sex trade. Her career began at 15 by playing closer to her own age, as the henpecked daughter of Téa Leoni and Adam Sandler in the movie "Spanglish"; more recently she was Catherine Keener's zit-obsessed teenager in the 2010 film "Please Give." For Ms. Steele the fun of playing younger roles is the opportunity to surprise audiences. "When you're an insecure teenager, you build walls and defenses and masks, and those are incredibly satisfying to perform and chip away at," she said. I mean, when I was an insecure teenager, you'd have had no idea what I was insecure about because I hid it so well. Only confident people are comfortable wearing their vulnerabilities on their sleeve. In spite of her girlish demeanor - 5 foot 1 and petite, with long, curly brown hair and a slightly high voice - Ms. Steele comes across as one of those confident people now. On a recent 95-degree afternoon, she suggested moving the interview from a stuffy Brooklyn cafe to her air-conditioned apartment nearby, and she had no problem telling a stranger that her bedroom would be best because the Freon was blasting from her window unit. Sitting cross-legged on her duvet, she displayed none of the fidgeting that she deploys to comic effect in "Slowgirl," an LCT3 production running through July 29. In it Becky visits the Costa Rican jungle home of her uncle Sterling (Zeljko Ivanek) after an accident back home has led to her suspension from school. Ms. Steele is so self-assured that Anne Kauffman, the "Slowgirl" director, was initially concerned about her ability to convey Becky's deep-seated anxiety. For one scene, when Becky is rattled at night by an iguana scampering on Sterling's tin roof, Ms. Kauffman tried to unsettle Ms. Steele by turning out the lights in the windowless rehearsal room. "There's a fundamental layer of fear in Becky, and Sarah has become so adept at playing these characters that we worked hard to find Becky's edginess," Ms. Kauffman said. Ms. Steele also filled a journal, writing out Becky's thoughts and fears, which Ms. Kauffman credited with "helping create a teenager who is distinct from others she's played." As dissimilar as actress and character seem, Ms. Steele said she related to Becky as the kind of girl she was once on a path to becoming. Growing up in Philadelphia with two accomplished parents, both doctors - her mother is the hematologist Katherine A. High - Ms. Steele rebelled as "a little hip-hop-dancing cute white girl who acted confident even if I wasn't." By the sixth grade she had become "a pretty bad girl," making out with boys for kicks and sneaking off with friends during a school trip in Virginia. Acting changed her. She joined a theater troupe whose members wrote their own shows to perform in Philadelphia schools; in it she met Gideon Glick, who turned out to be her neighbor and, eventually, a close friend who also became a New York actor. Ms. Steele began auditioning for bigger roles and beat out hundreds of other girls for the part of the chubby Bernice in "Spanglish." Filming in Los Angeles took several months, an experience that she said was transformative. "It was just so disorienting, gaining weight on purpose by eating McDonald's and even then wearing a fat suit at an age when no girl wants to be overweight," Ms. Steele said. "Téa Leoni said to me one day: "Don't come back to Hollywood after this. Go home, go to Harvard, then come back if you want. She was totally right. Back in Philadelphia she became a homebody, studious and a bit self-conscious about being recognized as "the girl from "Spanglish." " Taking Ms. Leoni's advice, she focused on preparing for college but ended up postponing study at Columbia University so she could appear with Cynthia Nixon in the Off Broadway production of "The Prime of Miss Jean Brodie" in 2006. The following year she starred Off Broadway with Mr. Glick in "Speech & Debate," the breakout play by Stephen Karam (a Pulitzer Prize finalist this year for "Sons of the Prophet"), while also starting at Columbia; she graduated last year with a degree in English. Scott Elliott, who directed Ms. Steele in both "Miss Jean Brodie" and "Russian Transport," said she was different from many young actresses because "she is just totally in touch with her emotions." Recalling working with her and the film actor Janeane Garofalo, who played the mother of Ms. Steele's character in "Russian Transport," he said: "Sarah's depth of emotion helped theater newcomers in the cast, like Janeane, find their own depth of emotion. Sarah played nerviness, she played sexiness, she played no vanity. Once she moves on to adult characters, I don't see a limit to what she will play. Ms. Steele said she felt no rush to abandon her teenage repertory, though she recalled that a friend who recently saw "Slowgirl" said he was "over me playing" 17-year-olds. The challenge, Ms. Steele said, is that she hasn't come across much great writing for twentysomething women. But she acknowledged that she hasn't seen "Girls," the HBO series by Lena Dunham about college graduates in Brooklyn. "People have said, "You and Lena Dunham would have such a bromance," " Ms. Steele said, laughing. All I do is watch the Sundance Channel. I really need to check out "Girls." "