“Beastly” is a modernized version of “Beauty and the Beast” that has no idea how to tell a modernized version of “Beauty and the Beast.” You have to admire the bravery of the filmmakers, who went ahead and made a movie despite not understanding the subject matter. It’s also pretty impressive that anyone could miss the point of “Beauty and the Beast,” which was intended to be understood by children. So really, kudos all around.

This surprisingly stupid teen romance, based on a novel by Alex Flinn, is set among the “Gossip Girl” crowd at a snooty New York private school. Kyle (Alex Pettyfer), the big man on campus, is rich and attractive, and he unabashedly uses those gifts to his advantage. Why pretend looks don’t matter when it’s so obvious that they do? His inattentive father (Peter Krause), a TV anchorman, taught him everything he knows about vanity.

Alex behaves cruelly toward Kendra (Mary-Kate Olsen), a goth chick who everyone says is a witch, and finally does enough to earn her wrath. She curses him, and instantly he is transformed from a handsome young man into a beast! (That’ll certainly put the kibosh on those “Kendra’s a witch” rumors.) Tattoos and scars cover his face, his hair is gone, and there’s a boil-like blemish near his nose. He is “hideous”! Which is to say, he is less beautiful than he used to be.

Unwilling to be seen in public, Kyle lets his dad buy him an apartment where he can be isolated, attended only by a talking clock and candlestick. No! I wish! He’s attended by a Jamaican housekeeper, Zola (Lisa Gay Hamilton), and a blind tutor, Will (Neil Patrick Harris), both of whom talk plenty but do not sing or dance or invite anyone to be their guest. Kyle has one year to get someone to love him in spite of his appearance, or else his condition will be permanent.

The beauty to our beast is Lindy (Vanessa Hudgens), a nice girl from school. (Don’t worry, she’s not rich, i.e., awful! She’s there on scholarship!) The story’s template, familiar to one and all, requires her to spend an extended period of time at Kyle’s “castle,” learn to love his inner beauty, and so forth. The problem? There is no plausible reason for Lindy to move into Kyle’s apartment. The solution? Eh, have her move in anyway.

Lindy’s father, a drug addict, is involved in a tragic crime that puts him and Lindy at risk for retaliation. Kyle, who likes to put on a hoodie and prowl the neighborhood anonymously, happens upon the scene and extracts a promise from Lindy’s dad: He’ll send Lindy to live with Kyle, where she’ll be safe and hidden, until everything blows over. If he doesn’t do this, Kyle will rat him out. OK, so Kyle doesn’t extract a promise so much as he blackmails the guy. Tomato, tomahto. The point is, now Lindy is living with a teenage boy, his housekeeper, and his blind tutor.

Kyle calls himself Hunter. Though he and Lindy have gone to school together for three years, she does not recognize his voice. Or his face, for that matter, which looks the same as before except now it has tattoos, a couple scars, and a blister. Nor does she make the connection that this “Hunter” materialized not long after Kyle mysteriously dropped out of school and disappeared. My point is that Lindy is apparently very dumb.

The message of this story is supposed to be that beauty is only skin deep and it’s what’s on the inside that counts. The movie claims to have the same point, yet carries it out in a laughably hypocritical fashion. In the book, Kyle really is a hideous monster, with claws and fur and everything. The film, adapted and directed by Daniel Barnz (whose Sundance debut “Phoebe in Wonderland” showed such promise), couldn’t go that route. Rendering Kyle as a truly ghastly figure would drive away the teenage-girl demographic, which would defeat the whole purpose in making the movie, which is to take money from teenage girls. And so we have a story about inner beauty in which everyone — even the ugly monster — is fairly good-looking.

In the original story, the beast demonstrates his selfless love for the girl by setting her free when she misses her father. In “Beastly,” Kyle lets Lindy go when she learns her dad is in the hospital — but Lindy was never being held captive in the first place! She could have left any time after the initial danger had passed. Since Kyle isn’t “letting” her go, he also isn’t proving to us that he has become a better person. And becoming a better person is the whole @*#&% point of the $@&(*# story!

Then there are the problems inherent in modernizing a fairy tale. Some details translate easily: a castle becomes an apartment, a prince becomes a rich kid, a singing teapot becomes a Jamaican housekeeper. Other elements are trickier to adapt for the real world, and “Beastly” screws it up almost every time.

Kendra uses magic to curse Kyle. So magic exists in this world … yet no one comments on it. Kyle’s first reaction ought to be: Holy crap, this goth girl LITERALLY just cursed me! If this is the real world — as opposed to a magical faraway kingdom where witches and fairies live — the very fact that dark magic is being used by high school students to punish mean boys ought to be of greater interest to the characters than it is. Zola, Will, and Kyle’s dad all accept what happened without question.

Kyle’s deformities do have a real-world quality to them. They look like real injuries that a person could really sustain. (Facial tattoos surely count as injuries, in addition to being a sad cry for help.) Assuming that Kyle chose not to dwell on the fact that a Brothers Grimm-style witch goes to his school, his first thought would be to have a doctor repair the damage. Tattoos can be removed; gashes can be sewn up; boils can be lanced. Hilariously, the movie addresses this fairly significant point by having Kyle and his dad talk to one (1) doctor, who says, basically, “We’re baffled, no idea what caused this, no idea why we can’t fix it.”

That’s it. One scene. In fact, it’s not even a whole scene. We come in just as the doctor is giving his diagnosis. As far as the movie’s concerned, that’s the end of that.

I want to see the movie where the doctor examines the shocking case of a healthy teenage boy who spontaneously developed tattoos and scars, then goes on to win acclaim in his field by writing about it in a medical journal.

So why doesn’t “Beastly” address any of these fundamental flaws in the storytelling? Laziness, I assume. Why bother? The target audience will be pleased just to see the girl from “High School Musical” in a romance, not to mention Alex Pettyfer with his shirt off (a state in which Kyle finds himself regularly). Whether it’s cheesy explodotainment like “Transformers” or simple-minded trash like “Beastly,” nobody ever went broke pandering to the lowest common denominator.

D (1 hr., 35 min.; PG-13, some profanity, brief mild violence.)