George, six years old and puny, put on a pair of heavy boxing gloves and squared off. "Good luck," he chirped at his sparring partner, a pudgy, middle-aged man with an embarrassed grin on his face. Then, summoning his fiercest look, George hauled off and belted his dad not once but twice, smack on the nose. His father, an eminent Boston psychiatrist, looked pained—but pleased.
George's triumph occurred recently at the Academy of Physical and Social Development in the affluent Boston suburb of Newton Center. A year and a half ago, the little boy was timorous, overattached to his mother, and the...