Even though the second movie in the "Diary of a Wimpy Kid" franchise is about Greg Heffley's seventh-grade year, a more fitting title would have been "The Sophomore Slump."

The first "Wimpy Kid" combined sixth-grade energy with graduate school insights into the anxieties and desires of preteen boys. It was smart when it needed to be, humorously gross occasionally and honest throughout.

The good qualities of the first movie show up only about half the time in "Rodrick Rules."

Greg (Zachary Gordon) and his best friend, Rowley, (Robert Capron) survived the first year of middle school and now face less ridicule and torment at school. Greg has an unrequited crush on the new girl, Holly Hills (Peyton List), and an ongoing battle with Chirag Gupta (Karan Brar), but that's nothing compared to what's happening at home.

The bane of Greg's existence in this movie is his older brother, Rodrick (Devon Bostick).

Rodrick seizes every opportunity to embarrass Greg publicly and blame Greg for his own mistakes at home.

Their mom, Susan (Rachael Harris), falls for all of Rodrick's tricks, while dad Frank (Steve Zahn) stays on the sidelines to make sure he doesn't incur Susan's high-pitched, obsessive wrath.

Susan just wants her boys to get along, so she tries a handful of ways to force Greg and Rodrick to bond. At first, this leads to more hazing for Greg, but eventually the brothers do begin to have some fun together.

Which leads to the polysemic title. Greg eventually discovers that Rodrick is pretty cool (he rules). But Rodrick also passes his rules for getting away with mischief down to Greg.

And here's the problem with the whole movie.

The "Wimpy Kid" movies are based on Jeff Kinney's hugely popular series of graphic novels. We call them "graphic novels" because they are in longer, bound form, but the fact is these are comics - brief episodes loosely tied together into novella length.

That's a difficult format to adapt, because we expect most movies to tell one unified story.

Think back to the Charlie Brown television specials. Most of that material came from Charles Schultz' "Peanuts" comic strips. In the best of those animated shows, like "A Charlie Brown Christmas" and "It's the Great Pumpkin, Charlie Brown," the writers melded Schultz' episodes into one story so seamlessly we might never guess they were based on several, separate comic strips.

The weakest Peanuts specials, like "It's Christmastime Again, Charlie Brown," make the source material painfully obvious.

That's exactly what happens in "Rodrick Rules." One scene will work then the next fails, and it's all disjointed. Funny scene, lame scene, lather, rinse, repeat.

It's a frustrating experience, because these are likeable characters in familiar situations. Kinney's sensibility is also desperately needed in a time when most entertainment for preteen boys is about warriors killing aliens or each other.

We want this movie to be good, but it consistently lets us down.

I came away with two questions.

First, why were these books adapted into movies, when their episodic nature would make so much more sense for the half-hour television series format?

Second, why didn't they structure the movie around Rodrick's rules? Instead of doling out the rules slowly in a way that might have tied everything together, Rodrick spews all of his rules in a quick sequence that lasts around five minutes.

The rest of the time, the movie meanders from one joke to another, until it hits a climax that doesn't climax at all. What is supposed to be the big, final joke is cringingly unfunny.

I hope there is a third "Wimpy Kid" movie since we need more entertainment for kids that's innocent, nonviolent, and helps take the sting out of adolescence. But I also hope the writers rediscover what made the first movie work.