Several studies that were directed towards examining the influence of cognitive factors in sex-related differences in mathematics achievement are reported. Specifically, two lines of research were pursued examining: (1) the relationship between different types of visual-spatial skill and mathematics achievement, and (2) the trainability of visual-spatial skill in junior high school students. Part I of this report discusses two studies that examine the relationship between mathematics achievement (including computation, algebra, and geometry) and visual-spatial skill. The results of the two studies indicated that visual skill and spatial orientation skill are somewhat distinct and both contribute to predicting mathematics achievement. Further research examining the development and trainability of these skills is promoted. Part II focuses on visual-spatial training research that was carried on in 1977-1980. The 1979-1980 investigation is the focus, with the two earlier years of work ending with negative results. This earlier work is documented in the hope that others may profit in reading about these experiences and conclusions. (MP)