The script of the high school comedy “Easy A,” by Bert V. Royal, is like Diablo Cody on steroids. It seems that every line is a joke, delivered by characters so nimble and articulate (except for the villains, of course) that they barely resemble real human beings. The effect can be exhausting, rather like being persistently jabbed in the ribs for a couple of hours by the person next to you to emphasize how funny everything is. But that doesn’t mean that the picture isn’t amusing. It is, just in an artificial, overly insistent way.

As a high school variant of “The Scarlet Letter” trying to do for Hawthorne what “Clueless” did for Austen, it also stretches one’s suspension of belief to the utmost. Emma Stone stars as Olive, a smart, good-natured girl who’s fortunate enough to have unbelievably “with it” parents—Rosemary (Patricia Clarkson) and Dill (Stanley Tucci). She also has a troublesome best friend, Rhiannon (Aly Michalka), who keeps hectoring her about her lack of a love life. So for Rhiannon’s benefit she invents a date with a college boy that supposedly went all the way. Before long, the story is all over campus, and she’s been transformed from an almost-invisible ordinary kid to the campus bad-girl, who sports a big red “A” as an accessory on her newly-sewn, highly revealing outfits. That earns her the condemnation of Marianne (Amanda Bynes), the judgmental, holier-than-thou leader of the powerful Jesus freaks.

It also attracts the attention of sweet Brad (Dan Byrd), a gay guy tired of being brutalized by the jocks, who asks Olive to help him by pretending to have sex with him at an upcoming party—something that will automatically give him straight credentials. She reluctantly agrees (though it’s hard to believe that Brad’s overdone macho swagger would convince even the dullest football player), and soon other guys low on the school’s social ladder are asking her for similar aid—and “paying” her with gift certificates and cheap coupons. She’s even made the scapegoat when Marianne’s boyfriend (Cam Gigandet) contracts a STD—though somebody else is actually the culprit. Also involved in the campus mix are the school’s hippest teacher (Thomas Haden Church), whose reading list just happens to include Hawthorne; his wife, guidance counselor (Lisa Kudrow), and the gruff principal (Malcolm McDowell). And, of course, there’s Olive’s true love, the guy she’s always pined after from afar—the equally sweet, hard-working Todd (Penn Badgley).

What scripter Bert V. Royal and director Will Gluck are after here—as Olive’s cute (and nearly wall-to-wall) narration, as well as the clips inserted periodically from pictures like “Sixteen Candles,” “The Breakfast Club” and “Ferris Bueller’s Day Off” make clear—is a contemporary John Hughes movie. But “Easy A” lacks the humanity that, however “cool” the surface, animated those pictures. It’s entirely synthetic, with a set of parents for Olive that essentially replace the unbelievably precocious kids that are standard-issue in sitcoms and a vision of extraordinarily powerful Christian fundamentalism in public schools that’s fine for jokes but out of whack with reality.

Of course, that doesn’t mean it can’t be enjoyable to sit through, because Royal does write clever lines and Gluck gives the movie enough momentum to get it by the plot contrivances. And the cast is excellent. Even if Stone is much too attractive and animated to be convincing as a girl initially overlooked by her classmates, she’s got energy and personality to burn, and though Clarkson and Tucci are playing parents as far removed from the clueless dolts who usually populate high school movies as you can imagine (and are equally unbelievable), the nail the parts through sheer professionalism. MacDowell makes a fine curmudgeon, too, and though Church and Kudrow aren’t given the best material, they’re able enough to make the most of it.

Among the youngsters, Bynes plays the chilly, purse-lipped stereotype of the sharp-tongued fundamentalist as well as anybody could, but Michalka is disappointingly shrill as Olive’s turncoat BFF. The guys are a fairly innocuous bunch, with Badgley blandly pleasant, Gigandet straightjacketed in a silly role, and Byrd overdoing the closeted gay bit. Technically the picture is top drawer, from Michael Grady’s cinematography and Marcia Hinds’ production design through Mynka Draper’s costume designs.

Final exam? In the high school comedy sweepstakes, “Easy A” doesn’t wind up at the top of the class, but it deserves a passing grade.