Grade: B

The old fable about the boy who cried wolf has been refashioned on screen so often by now (one of the niftiest versions was the 1949 thriller “The Window”) that a new variant hardly seems a very promising prospect, especially when it’s turned into a teen comedy. But “Big Fat Liar” confounds expectations and turns out to be one of the happiest surprises so far this year–an amusing, pleasantly old-fashioned piece enlivened by a good cast (even if they play too broadly at times) and boasting some clever bits. Amazingly enough, in a day and age when live-action pictures aimed at young audiences seem to exist on a stream of gooey substances and mild potty jokes, this effort from writer Dan Schneider and director Shawn Levy–both alumni of the Nickolodeon Network–happily eschews that sort of stuff and coasts along on a wave of good, clean fun.

The plot of the movie is hardly ground-breaking. Fourteen-year old Jason Shepherd (Frankie Muniz) is a prolific teller of tall tales who employs his overly active imagination and ready tongue to trick teachers and parents alike. When one of his scams gets him into so much trouble that he’s threatened with having to repeat a class in summer school, he pens a compensatory story called “Big Fat Liar,” about the trouble an addiction to falsehood can cause, that will earn him a passing grade; but in an admittedly contrived bit of business it’s appropriated by a Hollywood producer, Marty Wolf (Paul Giamatti), the nastiest man in Hollywood, as the basis for a potential summer blockbuster–which he desperately needs to save an endangered career. Jason’s father refuses to believe the boy’s tale about losing his work to a cinematic mogul and no longer has faith in his son (who’s put into a dreary hot-weather class), and so Jason and his girlfriend Kaylee (Amanda Bynes) travel to Hollywood to get the producer to admit what he’s done. Wolf’s refusal leads them to concoct a series of elaborate humiliations designed to persuade the producer to give in and restore his father’s trust in Jason; in the process they enlist the help of the many enemies Marty’s made in the business over the years. In the end, of course, Jason learns that honesty is the best policy and Marty gets his comeuppance.

Though the narrative might be trite, Schneider–himself a former actor–gives it enough little twists and shadings (and some nice Hollywood in-jokes) that it’s pretty consistently funny, and Levy shapes things quite skillfully (apart from moments like a musical montage when Jason and Kaylee try on costumes from a studio warehouse they break into–a sort of mugging contest that overstays its welcome). He doesn’t keep his lead actors in sufficient check, though, so that their performances, while basically good, tend to go too far over the top. Muniz and Bynes are both attractive, engaging kids with real talent, and throughout they remain extremely likable; but Muniz does pop out his eyes and seem a bit smug from time to time (it’s his “Malcolm in the Middle” shtick, which is better suited to the small screen), and Bynes sometimes takes the role- playing aspects of her character a bit far. Giamatti is even more unrestrained, chewing the scenery so ferociously that the very word subtlety seems to have disappeared from his thespian vocabulary; still, he gets the job done. The supporting turns by Amanda Detmer (as Wolf’s harried assistant), Donald Faison (as a chauffeur and would-be actor) and even Lee Majors (as an aging stuntman) are more laid-back; the same can’t be said of Jaleel “Urkel” White, who seems to be having a fine time lampooning himself as the star of Wolf’s latest big-budget debacle–but he gets some laughs.

What ultimately makes “Big Fat Liar” work is its general mood. Good-natured and easygoing (even the obligatory schoolyard bully is more benign than usual, and it’s pretty funny when he’s compelled to impersonate Kaylee to deceive her nearly-blind grandmother), the picture proves an amiable throwback to the earlier, better pictures of John Hughes, with a good deal of the charm of a “Sixteen Candles,” along with a milder variant of the slapstick violence familiar from “Home Alone.” (One will recognize shards of “Ferris Bueller” here, too–an older woman in a car who stalls traffic, the boring teacher whose droning delivery is reminiscent of Ben Stein’s.) The result is an energetic family flick that should appeal to the adolescent set while providing a good time for their elders, too.