The bad teacher in question is Elizabeth Halsey, who believes she's off to greener pastures until her wealthy, wimpy husband dumps her, sending her back to John Adams Middle School to make ends meet. Although she was apparently able to cross her T's and dot her I's in her first year with a life of luxury in her future, her second-year curriculum consists of sleeping and drinking while the class watches films about kids in class. Desperate for a way back out of teaching and into a suitor's cushy bank account, Elizabeth sets her sights on a boob job she's sure will do the trick.

Although "new tits" provide Elizabeth with some motivation, Eisenberg and Stupnitsky fail to make it feel like much of a relevant issue from scene to scene. Instead, the writing duo follows it down through a number of subsequent motivations and conflicts. The need for money leads to a simmering rivalry between Elizabeth and her "hall neighbor" Amy Squirrel (Lucy Punch), who is in charge of the school's yearly fundraising car wash and also the teacher who routinely scores a bonus for the highest standardized test scores. Said rivalry has the women fighting over the affections of Scott Delacorte (Justin Timberlake), a fellow teacher and heir to a watch-making fortune. And that courtship also makes room for gym teacher Russell Gettis (Jason Segel) and his repeated attempts to court Elizabeth, most of which involve poking fun at Scott.

Stacked up, these plots are almost Inception-like in their construction, and yet none of these stories feel like they're behind the wheel of the film. There's no doubt that Bad Teacher is often a funny movie, but without even a strong clothesline for the movie to hang on, there's no momentum or build to the progression of events. A scene where Elizabeth ends up at a student's house for Christmas dinner feels so divorced from the rest of the narrative it might've been lifted from another screenplay whole. Maybe Eisenberg and Stupnitsky were concerned that "dueling teachers" (the strongest and probably most relevant of these stories) would come off as too "sitcommy," but the alternative they've chosen -- nothing, essentially -- leaves the audience perpetually waiting for another shoe to drop, or for the film to just end.

Instead, the heroes of Bad Teacher are casting directors Anya Colloff and Amy McIntyre Britt, who have staffed Bad Teacher with an entire stable of reliable comic actors. Phyllis Smith (from "The Office") scores big laughs through indecision, and Thomas Lennon ("Reno 911!") has an amusing extended cameo as a school district employee. Fans of Segel will enjoy his performance here, which makes the most out of his somewhat limited screen time, and Lucy Punch walks the line between hilarious and insufferable as the kind of teacher who likes to put on costumes because she thinks the kids love it. Lastly, the film's MVP might be Eric Stonestreet ("Modern Family") as Elizabeth's roommate, who takes a role that seems like it must've been nothing on the page and executes it so well he makes exiting a room seem funny.

Putting all that works in the film together with all that doesn't and topped off with Jake Kasdan's completely neutral studio-comedy direction, Bad Teacher succeeds as a comedy but fails as a movie. You can take a bunch of funny gags and put them in the same movie, but if they don't have anything to do with each other, the film won't gain any traction. Bad Teacher is sort of like that: a funny premise that someone hung on a gag dartboard for talented comedians to come in and throw improv at rather than worked into a real movie. On a pass/fail system, it might squeak by, but it's less than the sum of its parts.