Reported are two separate but related longitudinal studies of two variables strongly associated with sex-related differences in mathematics achievement and enrollment, namely spatial visualization and confidence in learning mathematics. First, boys (N=33) and girls (N=36) in grades 6-8 who were discrepant in their spatial and verbal skills were interviewed to determine how they used spatial visualization in solving word and symbolic mathematical problems. Each subject was asked to read a problem, draw a picture to help solve the problem, and explain how the picture was used in the problem situation. In the second study, boys (N=31) and girls (N=32) in grades 6-8 who were above the mean in mathematics achievement and in lower or upper quartile in confidence in learning mathematics were interviewed about two question types (expectations and feelings), different perceived respondents (individual, peers, or teachers), and four mathematical situations (general, spatial, low, or high cognitive level). Among the results and implications reported are: (1) students with high spatial visualization skills tend to use them more than those with lower skills; (2) some differences were found in the ways boys and girls use their spatial skills, with girls who are low in such skills using them less than any other group; and (3) expectation of success in mathematics diminishes for girls from grade 6 to grade 8, while increasing for boys. In addition, technical information and instrumentation (including sample transcripts) are provided as separate reports in two detailed appendices. (JN)