Which is to blame, the Wizarding World and The Worst Witch? Or is it Once Upon a Time and Disney Channel’s Descendants? Either way, any film about reimagined fairytales and magic schools is perhaps doomed to struggle in a market already well stocked with spells and storybook characters.

That problem weighs heavy on this ponderous young-adult fantasy, adapted from the first in Soman Chainani’s series of books. While director Paul Feig (Bridesmaids, Ghostbusters) seems a good fit for Chainani’s theme of female friendship, the film’s fantasy elements arrive as a gaudy pageant of the over-familiar, made stifling by the sheer weight of world-building involved. Essentially, there’s enough lofty lore here to buckle Harry Potter’s broomstick.

After a blustery prologue, the story starts modestly enough with the bond between Sophie (Sophia Anne Caruso) and Agatha (Sofia Wylie), young misfits in the village of Gavaldon. While Sophie dreams of training as a fairytale princess at the mythical School for Good and Evil, Agatha has the makings of a witch. When a mysterious force whisks the duo to magic school, their roles are flipped. Is the sorting hat on the fritz, or does it know something we do not? Either way, Sophie is streamed into the school for Evil under Lady Lesso (Charlize Theron), while Agatha lands in the Good house under the beneficent watch of Professor Dovey (Kerry Washington).

While the friends’ attempts to fix this issue provide a solid storytelling spine, the plot soon loses focus. Faced with the demands of a secondary school story, expansive mythologising and a crowded intake of students, Feig and co-writer David Magee lean on exposition to navigate a muddled narrative, with deadening results. Making heavy weather of introducing the warring brothers – embodiments of good and evil – behind the school, the prologue alone groans with backstory.

Elsewhere, the dialogue labours the obvious. It’s the kind of film where characters are compelled to say, “I thought fairies were supposed to be nice” when encountering vicious variants, lest viewers failed to spot the twist. The students, similarly, deliver thudding banalities about their place in the storybook continuum. “My father, Captain Hook, he’s got a pretty awesome ship,” says one. “I’ll try not to be too charming,” says a prince, cheesily, when talk of “true love’s kiss” enters the picture.

Other gaps in plot are filled by Cate Blanchett’s voiceover, which gradually emerges as a character – or, rather, a quill called the Storian, a self-consciously writerly conceit that has the inadvertent effect of making the film seem dead on the page. The production designers do enliven proceedings in some aspects; the ‘Groom Room’ and other environs flaunt a kitschier front than the Potter saga’s tour of British castles, but the school is an extended Hogwarts otherwise, from forbidden forests to turrets, moats and great halls.