There’s something to be said for truth in advertising. After so many movies for tween girls that have basically been variants of the Cinderella story, this one is ready to admit its paternity. Unfortunately, praise for that bit of honesty goes only so far. Unfortunately, “A Cinderella Story” is more pumpkin than gilded coach, more smelly sneaker than glass slipper.

The picture is a lame attempt to update the musty old fairy-tale in the context of a typical high-school comedy. It thus gives viewers the worst of two worlds. On the one hand, it’s a limp retread whose every idiotically modernized turn is preordained. On the other it’s a formula teen flick that’s inept even by the standards of its cookie-cutter genre. There isn’t any magic in this “Cinderella,” literally or figuratively.

The supposedly sweet put-upon girl in this instance is Sam Montgomery (Hilary Duff), a cherubic Californian whose life seems perfect until her widowed dad marries a greedy shrew named Fiona (Jennifer Coolidge) with two daughters of her own and then promptly, and implausibly, dies in an earthquake. Eight years later, Sam is living in the attic of the house her stepmother inherited, treated as a servant by Fiona and her evil stepsisters (Madeline Zima and Andrea Avery), and compelled to work long hours in the fifties-style diner once named after her father but now called Fiona’s for its new owner. Sam does have pals–most notably the obligatory dweebish male chum, Carter (Dan Byrd) and the colorful staff at the diner, especially manager Rhonda (Regina King), but she’s an outcast at school, dissed repeatedly by catty campus queen Shelby (Julie Gonzalo). Even there, though, the bright girl has one solace–a bond with a on-line classmate-correspondent who calls himself Nomad, whom she met in a chatroom for would-be Princeton students. Neither knows who the other is–actually he’s Austin Ames (Chad Michael Murray), football quarterback and campus prince who’s secretly a sensitive soul and would-be writer being forced by his father to go to USC on a football scholarship–but they exchange constant chatter, until finally Nomad suggests that they meet at the Halloween dance. He goes as Prince Charming and she as Cinderella (in fairy godmother Rhonda’s wedding-to-be dress), and hit it off beautifully although he doesn’t recognize her. Of course she has to split by midnight to get back to the diner where she’s supposed to be working before Fiona and her stepsisters find her missing, and there follows a really tedious, badly thought-out morass of complications as Austin tries to discover Cinderella’s identity while finding the courage to reject his father’s plans for him, Shelby and Sam’s stepsisters plot to unmask her in the most embarrassing way, and Fiona schemes to keep Sam out of Princeton and in her thrall. There’s also a weird subplot about Carter’s pining for Shelby and linking up with her at the dance while he’s dressed as Zorro. Of course, ultimately everything works out–though in a completely forced and unfunny way. The wicked get their comeuppance and the good wind up happy. As Miss Prism once noted, that’s what fiction means. In this case, though, she would have said “bad fiction.”

The central problem in Leigh Dunlap’s woefully clumsy script is that every character in it is a dolt, and it’s impossible to have any sympathy for them or care what happens to them. Sam is a perky doormat, whom Duff plays with her usual breathless vacuity; Austen is a brainless wimp, so stupid that he can’t even recognize Sam though she’s wearing nothing more than a little eye-mask (that takes a greater suspension of disbelief than Lois Lane’s not recognizing Clark Kent as Superman), and Murray responds with a performance so laid-back that nothing is left on the screen but a blank countenance topped by a shock of tawny hair. Coolidge and Byrd both try much too hard to breathe some energy into their lifeless material; they’re both raging caricatures whose broad shtick grows ever more irritating as the movie drags on. The same is true of Zima and Avery, whose badly-staged slapstick routines are positively painful; Gonzalo is simply dull. The only person who emerges fairly unscathed is King, whose relatively restrained turn seems like genius in this company. One shouldn’t blame the cast too much, though; Dunlap’s anemic script, and Mark Rosman’s slack, untidy direction would sink anybody.

Visually “A Cinderella Story” aims for the bright, candy-colored look typical of these tween movies, but even in that department it comes up short, seeming a mite tacky and frayed around the edges. But that’s just the flavorless frosting on a dry, unpalatable cake. To hearken back to the far superior Disney version of the old tale, this movie is a bibbidy-bobbidy-bomb.