Steve Martin used to say it's impossible to be sad while you're playing a banjo, and I'm thinking it's equally hard to pull a long face in a roller rink.

"Roll Bounce," largely set in a rink during the late 1970s, is scruffy, but its characters are appealing, it conveys a warm sense of community and the soundtrack of old-school soul and disco - Bill Withers' "Lovely Day," Chic's "Le Freak," Taste of Honey's "Boogie Oogie Oogie" - could not be more infectious. Plus, the skating is sexy, athletic and thrilling.

Story-wise, there's too much happening in "Roll Bounce." Bow Wow, who remains little even though he dropped the "L'il" from his name, plays a kid who's grieving for his dead mom, whose dad is unemployed, whose friendships are changing and who is discovering girls (Jurnee Smollet, who was so vibrant in "Eve's Bayou," plays one of them). The storylines don't all pay off - there's a sense that quite a few scenes were left on the editing room floor - but what emerges from the too-muchness is a portrait of a neighborhood where families are hurting, healing and helping each other.

What emerges in the roller-rink is simpler. Everything builds to a Skate-Off, where the competitors include an arrogant, preening fop named Sweetness and where the action is as purely joyful as the K.C. and the Sunshine Band songs that accompany it.