Valerie Serrin still remembers vividly her anger and the feeling of helplessness. After getting a C on a lab report in an introductory chemistry course, she went to her teaching assistant to ask what she should have done for a better grade. The teaching assistant, a graduate student from China, possessed a finely honed mind. But he also had a heavy accent and a limited grasp of spoken English, so he could not explain to Ms. Serrin, a freshman at the time, what her report had lacked. "He would just say, 'It's easy, it's easy,' " said Ms. Serrin, who...