For all our snap-bracelet readiness to embrace girl power and its concomitant hashtags (#yougotthis!), depictions of preadolescents that are worthy of their subjects are thin on the ground. Perhaps because most tweens will just “watch up” anyway, big entertainment has slouched into a comfortable stance of pumping out cutesy kids’ content and edgy fare about high school, without bothering to give much thought to the beautifully messy middle ground. Are You There God? It’s Me, Margaret, writer-director Kelly Fremon Craig’s entry to the woefully underserved category of period dramas (make of that what you will), is destined to become a classic. Based on – but not entirely wedded to – Judy Blume’s seminal 1970 novel of the same name, the film is an entertaining comedy that also happens to be a stunning evocation of the fear and yearning that come with standing on the precipice of adulthood. Blume’s novel featured a half-Jewish, half-Christian protagonist who was questioning the existence of God while awaiting salvation via the arrival of her period, and eager to start wearing a bra. These preoccupations come to touchingly radical life in Fremon Craig’s funny-sad adaption, where entire minutes of footage are devoted to Margaret Simon trying on an absorbent pad or investigating different ways to sport a bra when her body does not require one. There’s little of the derivative about this film, which is largely thanks to Fortson’s incandescent performance at Margaret. She doesn’t play it cheesy or glib as she navigates life as an almost-there. Her eyes brim with wonder and wariness but the body part she puts to greatest use is her shoulders, which tell epics with their slumps and herky jerks. Here is a girl caught between childhood and adulthood, caring and not caring. The film opens with Margaret returning home from summer camp in New Hampshire only to learn that her family is moving from their New York City apartment to a New Jersey suburb. In the book, Margaret suspects that a large motivation for her parents’ decision to move is to separate from Sylvia, her overbearing yet fun Jewish grandmother. “She doesn’t have a car, hates buses, and she thinks trains are dirty,” Margaret tells us in the book. “So unless Grandma plans to walk, which is unlikely, I won’t be seeing much of her.” This sour note is glossed over in the film, but for good reason; Sylvia, played with oomph by Kathy Bates, is a lodestar of love and conspiracy. Other members of Margaret’s family are pulled to the fore in the film version, too. Her father, who can seem like a cardboard cutout of a suburban newbie in the book, comes to nebbishy life as played by Benny Safdie. Her mother, rendered by Rachel McAdams, is a revelation, nothing like the cloying type-A or cartoonish out-to-lunch artists that teens’ mothers tend to become on screen. Here is an artist who is depicted as an empath. Margaret’s mother is afforded a storyline of her own, and her struggle to circumvent the cliquish PTA scene and find her footing in the art world feels less like a B story than a satisfying cherry on top that mirrors Margaret’s fraught relationship to her changing world. McAdams pulls off portraying an early 1970s mother without a hint of the airless quality that is so common to historical dramas. Her expressiveness and softness of feeling sometimes make it hard to remember that this film is set in the Nixon era. World-building falls to production designer Steve Saklad and Ann Roth, the costume designer. While Margaret’s story is insular, it blooms to life thanks to their buzzy backgrounds and minty-fresh outfits. New York is a bustling retroscape that falls somewhere between the pulsating orbit of Mad Men and the sepulchral New York of The Squid and the Whale. Here is a safe cocoon of rotary phones, mushroom soup-reliant recipes and wood-paneled station wagons. The greatest decor might be found in the room of Nancy (Elle Graham, who’s nailed the queen bee who isn’t a B-word). A peer and neighbor of Margaret, Nancy hosts the all-girls’ secret club meetings for a contingent of Margaret’s sixth-grade class. Members must forswear socks, wear bras and spill the beans on all the important issues – namely boys and periods. Margaret and a friend visit the drugstore and purchase Teenage Softies sanitary pads – just in case. And then members of their group start having news to share. These sequences could easily be played for jokes, but when an important member of the gang goes to the bathroom at a fancy steakhouse and discovers that her time has come, the camera lingers on her crying in fear, and her staid Lilly Pulitzer-wearing PTA mom is unable to offer much in the way of help or warmth when she eyes her daughter’s underwear. “Oh! All right!” she offers crisply and no viewer in her right mind wouldn’t wish she could barge into the lavatory. When Margaret and her mom eventually find themselves in a bathroom under similar circumstances, the crying is of a different variety. It’s all terribly scary, yes, but in Blume and Fremon Craig’s hands, growing up is also heart-stoppingly beautiful. This adaptation is an answered prayer. Are You There God? It’s Me, Margaret is out in US cinemas on 28 April and in the UK on 19 May.