Tiffany Haddish and Kevin Hart in “Night School.” (Eli Joshua Adé/Universal Pictures)

Rating: 

There’s a genuine desire for self-improvement at the heart of the adult education comedy “Night School.” Yet, much as he did with “Girls Trip,” director Malcolm D. Lee tempers sensitive character development with gross-out humor. So the road to knowledge must first pass through bodily fluids.

Teddy (Kevin Hart) is a smooth-talking salesman who lives beyond his means, trying to impress his fiancee, Lisa (Megalyn Echikunwoke), by driving an expensive car and living in an apartment that he can’t really afford. A high school chum offers Teddy a job in finance — but first he has to go back to school to get his GED, and he doesn’t want Lisa to find out.

The movie humanely observes a group of people who, like Teddy, are struggling to improve their station in life. Coming from varied troubled backgrounds, the class dynamic is like a grown-up version of “The Breakfast Club”: Mackenzie (Rob Riggle) is the jock, Theresa (Mary Lynn Rajskub) is the nerd, and Jaylen (a hilariously paranoid Romany Malco) is the oddball.

With the exception of a teenager trying to avoid juvenile detention, Teddy’s classmates each harbor thwarted dreams or failed ambition, and their no-nonsense teacher Carrie (Tiffany Haddish) assures her students that there are no shortcuts. (The film, however, can take crude shortcuts to laughter, as when a frightened Jaylen vomits all over Mackenzie.)

Hart co-wrote the film’s script and isn’t afraid to joke about his own weaknesses — such as his height (Carrie calls him a “burnt leprechaun”). Despite expressions that can be over-the-top, Hart is perfectly convincing as a hustler and liar who knows deep inside that by making excuses he’s only cheating himself. You can feel the insecurity in his flashbacks to high school, and in his adult battles with Stewart (Taran Killam), the smart classmate who grew up to be a bat-wielding school principal. For her part, Haddish, while not nearly as volcanic as she was in “Girls Trip,” delivers the kind of tough love required of her role as educator.

At nearly two hours, “Night School” drags when the second act turns into a heist movie, and the school dances that should energize it slow it down — the excitement here is in its characters. But the movie gives some depth to its misfits, and ultimately sends the valuable message that nobody should be ashamed of who they are.

PG-13. At area theaters. Contains crude and sexual material throughout, strong language, some drug references and violence. 111 minutes.