Grade: B-

There are excellent messages about creativity, friendship, and learning to live with difference and loss in this adaptation of Katherine Paterson’s Newbery Award-winning novel of 1978. Unfortunately, other aspects of “Bridge to Terabithia” muddy the waters and make the whole less than totally rewarding. While a mostly sturdy adaptation of a much-loved book, it isn’t quite as secure a structure as it might have been.

The centerpiece of Gabor Csupo’s film is the camaraderie that develops between Jess Aarons (Josh Hutcherson), a boy from a hardscrabble rural family with a talent for drawing, and the new girl in town, Leslie Burke (AnnaSophia Robb), a spunky kid who moves in next door and demonstrates a vivid imagination and a way with written words. The two become best pals, joining forces against campus bully Janice Avery (Lauren Clinton) and—most importantly—inventing across the creek in the woods near their homes a magical kingdom, the titular Terabithia, where they contend with evil forces (representatives of the unhappiness in their real lives) and cement their friendship. (One can feel a kinship in this part of the plot with “The Witch, the Lion and the Wardrobe”—which is understandable, seeing that it comes from the same production company involved in “The Chronicles of Narnia” series.)

As drawn by scripters Jeff Stockwell and David Paterson and Csupo and played—very nicely—by Hutcherson and Robb, the relationship between Jess and Leslie comes across as genuinely warm and touching. The same can be said of Jess’ connection with his little sister May Belle (Bailee Madison, a real scene-stealer). And the realm of Terabithia is well realized—with excellent work by cinematographer Michael Chapman, who makes good use of the New Zealand locations, and solid visual imagery supervised by Jason Durey—even if the whys and wherefores of its elements seem quite arbitrary and a bit more subdued use of CGI might have been more appropriate to the story at hand, which sometimes tends to be overwhelmed by the effects.

In other respects, too, “Bridge” isn’t fully satisfying. The wider familial context is at best curious. Leslie’s parents, a couple of writers themselves, are portrayed as lost in their work and oblivious to their daughter except during the time away from their desks after finishing projects. And at home Jess is treated rather callously except by May Belle. His older sisters are simply nasty. His mother fobs off unsuitable hand-me-downs on him without blinking an eye. (The family is poor, but the lack of understanding or sympathy is palpable.) And most problematically of all, his father Jack (Robert Patrick) is less supportive than demanding and censorious. The character is supposed to be one of those dads who teach their sons responsibility through sternness, but for the most part he comes across as merely cold and remote, and his eventual exhibition of affection at a critical moment comes out of left field and doesn’t ring true. A subplot involving Jess’ infatuation with a music teacher (perky Zooey Deschanel) is rather oddly dealt with, especially when it plays a role in a major plot turn; and there’s what amounts to a sidebar Christian message—a visit to a church, and a later scene between the troubled boy and his father—that seems merely intrusive. The feel-good finale works rather too hard to inspire, too.

The end result of the digressions and miscalculations is a film that’s a mixed bag, with a solid core in the Jess-Leslie story but significant weaknesses elsewhere, both in the narrative department and the extravagant use of computer-generated imagery. One has to admire the respect and diligence with which the makers have approached the core of Paterson’s book, but you can almost feel the pull to the spectacular undermining the simpler, more humble story elements, and in the end the transformation from page to screen works only intermittently. So long as “Bridge to Terabithia” keeps to the straightaway it’s a sensitive children’s story with some fine lessons to impart; but questionable narrative detours and an overemphasis on visual effects make for a rather bumpy ride.