was so dour. In addition to detecting cheaters, the algorithm could also identify the best teachers in the school system. A good teachers impact was nearly as distinctive as a cheaters. Instead of getting random answers correct, her students would show real improvement on the easier types of questions they had previously missed, an indication of actual learn- ing. And a good teachers students carried over all their gains into the next grade. Most academic analyses of this sort tend to languish, unread, on a dusty library shelf. But in early 2002, the new CEO of the Chicago Public Schools, Arne Duncan, contacted the studys authors. He didnt want to protest or hush up their findings. Rather, he wanted to make sure that the teachers identified by the algorithm as cheaters were truly cheating-and then do something about it. Duncan was an unlikely candidate to hold such a powerful job. He was only thirty-six when appointed, a onetime academic all- American at Harvard who later played pro basketball in Australia. He   had spent just three years with the CPS-and never in a job impor- tant enough to have his own secretary-before becoming its CEO. It didnt hurt that Duncan had grown up in Chicago. His father taught psychology at the University of Chicago; his mother ran an after- school program for forty years, without pay, in a poor neighborhood. When Duncan was a boy, his afterschool playmates were the under- privileged kids his mother cared for. So when he took over the public schools, his allegiance lay more with schoolchildren and their families than with teachers and their union. The best way to get rid of cheating teachers, Duncan had decided, was to readminister the standardized exam. He only had the resources to retest 120 classrooms, however, so he asked the creators of the cheating algorithm to help choose which classrooms to test. How could those 120 retests be used most effectively? It might