Sex differences in spatial functioning are frequently the source of cocktail party conversation and entertaining cartoons. These anecdotes and images feature such figures as men who forge intrepidly into the wild armed only with a compass and an innate sense of direction and ditzy women who hold maps upside down and depend on the kindness of strangers. These figures of fun, although exaggerated, have some basis in truth. Studies using standardized tests have found support for the belief that men have strengths in the spatial domain, sometimes quite marked strengths. For example, the average American man has an ability to perform mental rotation of a threedimensional object that exceeds that of the average American woman by half a standard deviation or more (Linn & Petersen, 1985;Voyer, Voyer, & Bryden, 1995; for the statistically uninitiated, such differences are considered moderate to large and may well be obvious to the casual observer). There are similarly substantial sex-related differences on tests of mechanical reasoning, which involve a large spatial component (Feingold, 1995). Furthermore, and consistent with remarks made in January 2005 by Lawrence Summers, the president of Harvard University, these differences are often most 69