“Fish in a Tree” at New York City Children’s Theater pulls viewers into the mind of an 8-year-old girl with dyslexia, using projections and immersive sound design.At Theater Row in Manhattan, a gigantic notebook, filled with lines of type, stands open onstage. As the audience gazes at the pages, the letters refuse to stay still. They push together and pull apart, all the while bobbing like drowning swimmers.Rubbing your eyes won’t help. This moment from “Fish in a Tree,” a world premiere from New York City Children’s Theater, reveals the way a social studies textbook appears to Ally Nickerson, the play’s 8-year-old heroine. Although Ally doesn’t know it yet, she has dyslexia, a learning disability that, according to the Yale Center for Dyslexia and Creativity, affects 20 percent of the population.The goal was “to give our audience a real picture of what it’s like,” said Barbara Zinn Krieger, the company’s artistic director, who consulted more than a dozen experts on dyslexia while writing the show. Adapted from a 2015 best seller of the same title by Lynda Mullaly Hunt, “Fish in a Tree” relies on digital technology more than any other production in the company’s more than 25-year history. It focuses on Ally’s life both at home, where her brother has a secret of his own, and at school, where Ally, who has become a troublemaker to hide her disability, faces bullying from two girls.Although Ally is a sixth grader in the book, Krieger wanted her to be younger onstage, “especially when I discovered that the earlier you discover somebody has dyslexia, the better off the child is,” she said.Throughout the show, which opens on Saturday, Kylee Loera, the creative team’s video designer, uses the onstage notebook’s surface as a screen on which to show both still and animated images of Ally’s outer and inner lives: not only the pages she struggles to read, but also her family’s kitchen, her school, and her fantastical daydreams, or “mind movies.”But most of all, the notebook, which Ally calls her Sketchbook of Impossible Things, is the home for her artwork. (One of its blank pages is also outlined on the floor of Ann Beyersdorfer’s set.) In the sketchbook, which Ally carries with her, she draws fanciful creatures and encounters, which take shape onscreen overhead as the audience watches. And as Ally, portrayed by Lily Lipman, changes over the hourlong action — acquiring a diagnosis, a mentor and self-esteem — her art changes, too, shifting from black-and-white to color.As Ally changes over the hourlong action, her art changes, too, shifting from black and white to color.Sara Krulwich/The New York TimesIn devising an onstage gateway to Ally’s imagination, “We were like, what if the portal is actually her notebook?” said Sammy Lopez, the show’s co-director. “And what if we gave the audience the opportunity to jump into the notebook with Ally? And so that kind of inspired the ways in which we built out the physical life of the show.”Ally’s sketches, which she often draws during class, are by the illustrator Ben Diskant, who is dyslexic himself. He based some of the images on references in the novel, like boxing lobsters and a small fish with wings. (The work’s title comes from a quotation attributed, probably falsely, to Einstein: “Everyone is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”) Diskant, however, also contributed his own ideas, sketching animals because, he said, he has always found their lack of language comforting.Drawing “has set me free creatively from having to explain myself in any written form or any verbal form,” he said, adding, “and so I really relate to Ally in that way.”Loera designed the imagery for Ally’s “mind movies.” As these adventures unfurl onscreen, or, in one case, as shadow puppetry, the show’s young adult performers, who also play Ally’s third-grade classmates, teacher and brother, simultaneously act them out. For instance, Ally sees herself being jailed in her imaginary film “The Prisoner.” As her schoolhouse morphs into a prison in the projection, Louis Baglio, in the role of Ally’s new teacher, Mr. Daniels, adopts clothing and props to become a Wild West sheriff. (This all occurs comically to the strains of the theme from the 1966 western “The Good, the Bad and the Ugly.”)“We have to teach our young audience that, during this play, you’re going to see the players create, you’re going to see them step into Ally’s mind,” said Melissa Jessel, the production’s other co-director. Music, she added, “really helps to engage.”From left, Sadie Veach, Fernando Mercado, Lipman, Louis Baglio and Madison B. Harris. The actors who play Ally’s classmates and teacher also double as characters in the imaginary sequences Ally creates.Sara Krulwich/The New York TimesIn addition to film-score excerpts and a musical theme that serves as a bridge between Ally’s reality and her imaginings, Glenn Potter-Takata, the production’s sound designer, uses a buzzing noise to accompany Ally’s dyslexia-associated headaches. Occasional voice-overs — “Why, why, why can’t I read like everyone else?” — further disclose her thoughts.The show’s creators also added detail and texture to the novel’s explanation of the condition. A dyslexic teacher Krieger consulted described it as like trying to extract information from mental filing cabinets, but selecting it in the wrong order. That analogy went into the script.So did up-to-date tools for dyslexic students, which the show’s dramaturge, Taylor Janney-Rovin, an educator who instructs dyslexic children at Valence College Prep, in Queens, suggested. Mr. Daniels, whose help Ally finally agrees to accept, introduces Ally — and the audience — to multisensory techniques for children with learning disabilities. These include skywriting — writing letters large in the air — and drawing words in shaving cream.Krieger continued to modify her script drafts in response to internal feedback. (In the cast, creative team, company management and staff, there are seven people with disabilities.) She had invented an encouraging statement from Ally’s grandfather, “Anything is possible if you try hard enough.” Lipman, who is on the autism spectrum and has an auditory processing disorder, objected to this wording for its implied burden on those in similar circumstances. Krieger rewrote the line as “Many things are possible if you believe in yourself.”Lipman approved the revision. “The biggest moment for me is when Ally’s like, ‘So there’s a reason why I can’t read,’” she said. Her character realizes that her classmates have an advantage, Lipman added, and “it’s just that I didn’t get that piece that they all got.”The play, however, is not intended just for young people with disabilities. Its examination of bullying, friendship and sibling bonds is geared toward a larger audience, as is its wide embrace of creativity.The company’s hope, Jessel said, is that “children walk away from the story interested to explore their own imaginations.”Fish in a TreeThrough April 9 at Theater Row, Manhattan; nycchildrenstheater.org. Running time: 1 hour. More