It starts with a punch in the face as two giggling, gassed-up 'tween-age girls huff nitrous oxide from whipped-cream cans and smack each other around for kicks. "Harder," they scream, laughing. "I can't feel anything!" It's a shock effect worthy of Larry Clark, but production designer-turned-director Catherine Hardwicke's first feature manages to skirt cheap sensationalism. And what it lacks in subtlety it more than makes up for in impact; it's one of the most honest and harrowing looks at female adolescence ever to reach the screen. Thirteen-year-old Tracy (Evan Rachel Wood) and her older brother, Mason (Brady Corbet), live in suburban L.A. with their mom, Melanie (...