The high-energy, socially progressive 1980 movie is now a low-wattage, borderline-racist stage musical that plays like a parody of an after-school special, with no stereotype untapped. Must the Latino students do a flamenco number? Must the black dancer perform an insipid rap about growing up around crack deals? Must the girl named Katz say ''Oy vey''? And apparently no one in the arts is gay. (Although there are hints about one blond hunk, he gets a duet and kiss with Katz before the finale.) Aside from the title song and teacher Cheryl Freeman's showstopper ''These Are My Children,'' the tunes aren't gonna live forever. The hardworking young cast could learn a lot from Freeman's showmanship.