THE DUFF ★★☆
(M) Selected cinemas (101 minutes)

Teen movies often focus on belonging, on the relationship between the outsider and the in-group: from The Breakfast Club to Disturbing Behaviour to Mean Girls, critiquing the power of clique is an established, intriguing focus. The DUFF, written by Josh Cagan and directed by Ari Sandel, looks at first as if it's set in a post-clique world, where it's ok to be niche. But no, the film tells us, for jock, goth and geek alike, there's another hurdle: you need to be hot.

Not a revolutionary concept, you might think. But there's more: the film highlights the existence of the DUFF, the "designated ugly fat friend", a sidekick who makes the people around him or her look good. As a well-meaning jock, Wesley (Robbie Amell), explains to the gobsmacked Bianca (Mae Whitman), that to qualify as a DUFF you simply have to be less attractive than your friends. And he has no doubt that she fits the bill.

Bianca is an eccentric, in teen movie terms – she's smart, she's articulate, she wears overalls, she's a horror movie fan. Yet she doesn't really interrogate the notion of the DUFF; instead, she severs all ties with two close girlfriends from whom she has been hitherto inseparable.

She decides to do a deal with Wesley, her next-door neighbour whom she has known since childhood: she'll help him with his chemistry exams (so that he can keep his football scholarship) if he'll help her smarten herself up so that she can score a date with Toby (Nick Eversman), the sensitive, guitar-strumming dreamboat she yearns for.

The course of the story has very little to do with the gimmicky notion of the DUFF, which is really a kind of McGuffin, Alfred Hitchcock's term for a narrative device that the protagonist pursues or is motivated by, but isn't actually important to the overall story. The movie is really all about the relationship of the unlikely couple, and the actors are the most appealing element of the film: Whitman (Arrested Development) is ebullient and engaging as a contrary figure and Amell does well as the sensitive jock, although he doesn't quite reach the benchmark set by Channing Tatum in She's the Man.

Most of the other teenage characters – above all Wesley's on-and-off girlfriend, Madison (Bella Thorne) – are one-dimensional figures whose function is to drive the plot. Even the supposed best friends (Skyler Samuels and Bianca Santos) are broad-brush figures.

A couple of the adults fare better: Allison Janney, as Bianca's mother, who found a post-divorce career as a self-help guru, has some nice moments but her foray into internet dating is raised and then unceremoniously dropped. Ken Jeong (Community, The Hangover) and Romany Malco (Weeds) as the hapless principal, have brief comic roles.

The DUFF, tricked out with social media references and preachy intentions, turns out to be more than a little hypocritical; by the time we get to Bianca's prom appearance, all pretence of originality is abandoned.