A two year longitudinal cross-sectional project investigated the determinants of students' decisions to enroll in advanced mathematics courses, with particular attention to the determinants of sex-differentiated course participation. This study attempted to: (1) plot developmental shifts on psychological variables related to achievement attitudes; (2) assess the relative importance of these variables for student decision; and (3) identify the developmental origins of individual differences on these variables. Questionnaires were administered to approximately 600 students in grades 5 through 12, their parents, and their teachers. School record data and observational data were also gathered in the first year of the study. Students' estimates of their mathematical abilities, their estimates of the value of advanced mathematics, and their perceptions of their parents' beliefs about their mathematical ability decreased with age. Students' estimates of the difficulty of mathematics increased with age. Plans to continue in mathematics were facilitated by high expectancies, high self concept of mathematical ability, and low estimates of future course difficulty. Sex differences favoring boys were found on each of these scales. In general, mothers had the greatest influence and fathers had the least influence on students' attitudes regarding mathematics. Teachers' influences were intermediary. (Author/CTM)