"The DUFF" isn't exactly a new milestone in teen-comedy filmdom, but it is capable, spry, and mostly wise when it isn't spelling out its moralistic intent. For a subgenre that has been starved for fresh blood in recent years—one of the last great ones was 2010's classic-in-training "Easy A"—musty conventions somehow don't seem as worn-down as they once grew to become after post-John Hughes, late-'90s/early-'00s saturation levels had run their course. Adapted by director Ari Sandel and screenwriter Josh A. Cagan (2009's "Bandslam") from Kody Keplinger's 2010 novel, "The DUFF" follows many of the well-predicted hallmarks of its brethren, but tackles them from a timely here-and-now setting that will likely ring true for modern high-school-aged audiences. And, if the film owes its everything to "Sixteen Candles," "Some Kind of Wonderful," "Can't Buy Me Love," "She's All That," "10 Things I Hate About You," and "Mean Girls" (just to name a few), at least its story stays true to its irrepressible heroine without feeling the need to change her. Not bad for a movie with multiple makeover montages.

Malloy High senior Bianca Piper (Mae Whitman) marches to the beat of her own drum. She loves writing for the school newspaper. She has two wonderful best friends in the popular, kind Jess (Skyler Samuels) and Casey (Bianca Santos). Although she is inexperienced with the opposite sex and hasn't much fashion sense, she never is made to feel like an outsider by the people whom she trusts the most. And then, just like that, her reality is shattered forever when her hot-shot neighbor and classmate, football captain Wesley Rush (Robbie Amell), informs her that she is a DUFF (Designated Ugly Fat Friend)—that is, the catch-all phrase for an approachable, non-threatening person whom people go through to get close to their hotter friends. Suddenly feeling insecure and taken advantage of, Bianca drops Jess and Casey as her BFFs, then makes a deal with Wes to tutor him in chemistry in exchange for teaching her how to be more cool and confident. On her path to gaining the courage to ask out her musician crush, Toby (Nick Eversman), she finds herself becoming the subject of snotty queen-bee Madison's (Bella Thorne) wrath after the junior tyrant catches her getting too close to on-again-off-again boyfriend Wes.

"The DUFF" isn't as satirically piercing as "Mean Girls" or "Election," but its acerbic sense of humor is pert and polished. While the act of coming of age is universal, the increased stresses of today's technologically advanced, social media-savvy teens include cyberbullying and the indignity of not only cutting ties with a friend or significant other in person, but also having to do it all over again on Twitter, Facebook, Instagram, Tinder, etc. The characters are a grab-bag of archetypes and surprises. The nasty Madison is pretty irredeemable (when she tells Bianca that she's tried to be nice to her after spending the whole film terrorizing her, Bianca searchingly replies, "Have you?"), but Bella Thorne (2014's "Blended") exhibits solid comic flair in the somewhat thankless role. If a part of Jess and Casey were aware of the "DUFF" analogy before it came to their attention, that doesn't mean they don't genuinely like Bianca and value her as a friend. Meanwhile, Wesley proves to be more than a dumb jock, his lack of a filter both a downfall and the whole reason Bianca experiences a much-needed awakening to what has been going on under her nose. Less believable is why he would continue to hang around someone as unpleasant and vapid as Madison, let alone entertain the thought of getting back together with her.

Mae Whitman (2012's "The Perks of Being a Wallflower," TV's "Parenthood") has been an MVP supporting player her entire acting career, going all the way back to her unforgettable performance as Meg Ryan and Andy Garcia's youngest daughter in 1994's "When a Man Loves a Woman." It has taken twenty-plus years, but finally Whitman has been given the chance to be front and center in the lead role. If her unabashedly charming, irresistibly touching turn as Bianca is any indication, her star has finally begun to bloom. Intuitive, chameleonic and innately relatable, Whitman is unlike anyone else in her age range—a rarified quality that should hopefully serve her well in the future. The chemistry she shares with Robbie Amell (2005's "Cheaper by the Dozen 2"), as Wes, is always there; even when the two are sparring, there is an unspoken connection pulling them closer. Amell, he of an undeniable megawatt smile, reminds of a young Tom Cruise. As Bianca's pals, Jess and Casey, Bianca Santos (2014's "Ouija") and Skyler Samuels (2009's "The Stepfather") are refreshingly written as caring and respectful, though their lack of depth and unique personality traits means that they become rather interchangeable. Allison Janney (2014's "Tammy") is always a welcome face, and she steals a number of her scenes as Dottie, Bianca's divorced-mom-turned-self-help-guru. She and Whitman play so well off each other, one wishes they had a couple more scenes to flesh out their mother-daughter relationship.

"The DUFF" flirts with, and falls trap to, certain tried and true teen-movie staples. There are the complete opposites who live next door to each other and start to fall in love after making a pact to help each other out. There is the mean girl whose job it is to make our protagonist's life a living hell. There is the embarrassing hidden-camera footage that leaks to the whole school. There is the big climactic dance where truths are revealed and conflicts come to a head. The nice thing about the film, though, is that director Ari Sandel keeps things mostly grounded in authenticity, particularly when it comes to the treatment of Bianca. She is not a nerd, and no one ever accuses her of being fat or ugly. If she doesn't live up to the stick-thin, 5'10" standards of female beauty, she is okay with that. Even while flirting with new hairstyles or getting up the nerve to try on different clothes, Bianca stays true to who she is. It is a valuable message that comes through loud and clear—so clearly, in fact, that the film would have been better to reel back a late scene where she lays out everything she has learned about the importance of accepting oneself. Do Bianca and Wes have a future together? On paper, they do not seem right for each other, and yet when put together they somehow fit. "The DUFF" isn't inventing a new filmic language, but it lives up to its promises and doesn't talk down to viewers. The main attraction is Mae Whitman, acting her heart out while making her every last moment look as natural and vulnerable as that of a real life being lived.