Not having read “The Diary of a Wimpy Kid,” I can’t speak to its quality as children’s literature. But the film adaptation is no better than a run-of-the-mill made-for-cable movie on any network that caters to pre-teens. And it has one insurmountable flaw: its lead character is a obnoxious little jerk whom even an ingratiating tyke like Zachary Gordon can’t turn into a sympathetic character. When Greg Heffley’s threatened by bullies or his classmate nemesis, a snooty girl, your reaction might be “Get him!” Which is not, I think, what the makers intended.

Greg’s a fresh-faced kid starting his first day in middle school. He’s saddled with a typically awful family. Dad Frank (Steve Zahn) is an ineffectual boob, and Susan (Rachael Harris) a mom who pays too little attention to him. She’s too busy dealing with Greg’s older brother Roderick (Devon Bostick), a thoroughly repulsive would-be rocker who spends most of his time tormenting the kid, and toddler Manny (Connor and Owen Fielding), who occasions a good deal of the potty humor children’s movies seem to require nowadays. (Director Thor Freudenthal, who had much better luck with the pleasant “Hotel for Dogs,” also uses him for the “cute” reaction shots that canines ordinarily provide in movies.)

Greg’s ambition is to be a popular success in school, but everything he tries is a disaster. He joins the wrestling team, for example, and finds himself bested not only by the geeky class shrimp, Fregley (Grayson Russell), but by his odious rival Patty (Laine MacNeil), whose hostility toward him—it turns out—is explicable (even in kindergarten he was a jerk, dubbing her Patty the Fatty). The only thing Greg has going for him is the friendship of long-suffering pal Rowley (Robert Capron), a chubby, good-natured lad who’s always done his bidding with a smile and supported him unconditionally. But—and here’s the kicker—Greg doesn’t hesitate to stab Rowley in the back when it suits his own desire for acceptance (which, of course, he doesn’t deserve). And the fact that he tries to make up for it in the end isn’t really enough to redeem him.

Maybe in the form of a real diary, illustrated with the simple stick drawings the movie sometimes uses in animated interruptions, “Wimpy Kid” has real charm, and the message about being true to yourself rather than trying to remake yourself for popularity’s sake isn’t a bad one. But if so, it’s been pretty much lost in this mostly-live action adaptation, which Freudenthal directs flatly, without any sense of rhythm or consistent tone, and which the cast—except for Gordon and Capron, who have a nice rapport—treat with a ghastly overemphasis that’s apparently intended to pummel you into acceptance. Nor does the movie look particularly good; it has the cheesy appearance of a Disney Channel flick, and Jack N. Green’s cinematography too often gives the images a glare that’s not just unattractive but exhausting to the eye. And Theodore Shapiro’s endlessly perky score is no help (and we certainly didn’t need the awful dance sequence involving Rowley and Kaye Capron, “playing” his mother).

Boys of a certain age—six to ten, perhaps—may enjoy “Diary of a Wimpy Kid.” It has plenty of the dumb slapstick and slightly naughty gags (like booger humor) they seem to dote on. And fans of the book may give it a pass, especially since it makes occasional use of the drawings. But compared to outstanding children’s films, it’s certainly no keeper.