To explain the improvement in scores, Hall told the investigators that “an effective teacher three years in a row will completely close the gap between a child born in poverty and a child born to a middle-income family.” This theory, in its earliest form, derives from a study by William L. Sanders, a statistician formerly at the University of Tennessee, but the findings, which have contributed to a nationwide effort to rate teachers rigorously, have been overstated to the point of becoming a myth. According to a recent statement by the American Statistical Association, most studies show that teachers account for between one and fourteen per cent of variability in test scores.
John Ewing, who served as the executive director of the American Mathematical Society for fifteen years, told me that he is perplexed by educators’ “infatuation with data,” their faith that it is more authoritative than using their own judgment. He explains the problem in terms of Campbell’s law, a principle that describes the risks of using a single indicator to measure complex social phenomena: the greater the value placed on a quantitative measure, like test scores, the more likely it is that the people using it and the process it measures will be corrupted. “The end goal of education isn’t to get students to answer the right number of questions,” he said. “The goal is to have curious and creative students who can function in life.” In a 2011 paper in Notices of the American Mathematical Society, he warned that policymakers were using mathematics “to intimidate—to preëmpt debate about the goals of education and measures of success.”