Channing Tatum got a leg up on stardom in 2006 with "Step Up," an otherwise humdrum flick cashing in late on the hip-hop dance craze.

Tatum was wise enough to step aside from the franchise and wannabes stepped in, becoming never-will-bes. (Rick Malambri and Robert Hoffman, anyone? Anyone?) Now, in a fourth "Step Up" chapter nobody clamored for, Ryan Guzman is the latest dancing hunk that doesn’t appear to have a "Magic Mike" in his future.

The young cast of "Step Up Revolution" is mostly like Guzman: unknown and trendily coiffed, ripped or fetching enough to be considered talented by less discerning audience members. The kids are lithe, limber and can’t act worth a lick. But that isn’t the point of "Step Up Revolution," which exists only to display hard bodies in tribal vibration in 3-D. Even that gimmick can’t make one-dimensional characters interesting.

There is an attempt at devising a plot. Sean (Guzman) leads a multicultural band of Miami pranksters in flash mobs, those impromptu dance routines never played as slickly elaborate as they do here. The Mob, as they’re called, hopes to become famous by getting 10 million hits on YouTube, which is the true measure of fame these days.

Sean meets Emily (Kathryn McCormick), a classically trained dancer who needs more edge in her performance to gain admittance to a snooty academy. Sean is all edge, so it’s a match made in Screenwriting 101. Emily’s father (Peter Gallagher, who doesn’t dance) is a real estate magnate developing a billion-dollar complex in the Miami neighborhood the Mob calls home.

The Mob becomes "artistic vigilantes," staging routines to disrupt those plans and deliver a "message" that gets lost in the glare of flash pots and a blaring techno beat. Forget those lessons the right people will learn, and the inevitable romance against hastily stacked odds. "Step Up Revolution" is all about the dancing, and it’s occasionally spectacular.

Flash mobs at a swanky museum, making art come to life, and a synchronized satire of corporate greed are very entertaining. The one beginning with a smoke bomb tossed into a crowd, followed by intimidating stompers wearing tactical gear, is less so.

"Step Up Revolution" is a bad movie with a few good moments, usually when the cast sets aside delusions of acting prowess and does what comes naturally to them, which is to look pretty and perform smartly choreographed seizures.