At the Goodtime Chinese School in the Bethany suburb of Portland, Oregon, an American child stops school director Zhou Yanzhuo, of China, in the hallway to ask a question in English. She requests that he speak in Chinese and the third grader, who has no Chinese heritage, handily switches languages. The child is one of several dozen students attending rigorous summer classes for Chinese language instruction at an age when experts believe language acquisition is easiest. While American...