This study was designed to analyze some performance factors as a possible source of sex-related bias in psychometric tests of visuospatial aptitude. Goldstein, Haldane, and Mitchell (1990) explored the effect of two response styles-slowness of performance and reluctance to guess-by using a 3-D mental rotation test (the task showing the largest cognitive sex difference) and found that time limits and raw scores contributed substantially to the male advantage. We applied two tests in the speed-power continuum to a representative sample of 621 males and 821 females in their last year of high school in a 2 x 2 (gender x time) full factorial design. Reluctance to guess was similar for males and females. Males obtained more correct responses on both tests, and for both time conditions, than did females. These results are not only statistically significant but also are of substantial practical consequence.