Riffraff

``Even as a baby, Sophia had been a nuisance,'' and now she has grown into a loud, obnoxious and absolutely unflappable girl, the terror of her neighborhood. Sam, in contrast, is ``so shy that when he saw someone he knew . . . he'd duck behind a tree or fence or a telephone pole so they wouldn't see him.'' Not surprisingly, neither of these singular characters has a thriving social life. Through their mutual acquaintance with Theodore Snackle, who hates his name, and whose nose, as Sophia points out thoughtlessly, ``would look good on a witch,'' Sam and Sophia both learn something about the nature of friendship and find that they are destined to be pals. Clarke ( The Heroic Life of Al Capsella ) goes easy on his novel's message, focusing instead on the extremes of behavior that lead Sophia and Sam into their relationship. Calling to mind both Pippi Longstocking and the novels of Beverly Cleary, this humorous import from Down Under is a welcome addition to the ranks of comical middle-grade stories. Ages 9-12. (Dec.)