In this dissertation study, I aimed to 1) investigate gender patterns in students' career aspirations, in both STEM and non-STEM fields, and 2) identify factors contributing to persistent gender differences within specific STEM disciplines. Drawing on Gottfredson's (1983) model of circumscription and compromise, I examined gender patterns and shifts in students' career aspirations. Additionally, Eccles's expectancy-value theory (1981) was adopted to examine the influence of achievement and motivational factors, particularly in mathematics and science, on gender differences in STEM-related career aspirations. Specifically, I investigated the relationships among students' math and science achievements, attainment values of math and science tasks, and students' STEM-related career aspirations. Furthermore, I explored the role of cultural beliefs, primarily gender stereotypes, in shaping math and science motivations of girls and boys, potentially leading to distinct pathways in STEM careers. I used data from the High School Longitudinal Study of 2009 (HSLS:09) to examine gender patterns in students' career aspirations and to analyze the relationships among gender, academic achievement, motivational factors, and career aspirations. The results revealed significant gender disparities in STEM career aspirations, with boys expressing a preference for career fields of physical science, engineering, mathematics, and computer science, while girls expressed a preference for fields of social, life, and health sciences. The results also highlighted the complexity of students' career development. For example, the results emphasized the importance of students' mathematics and science motivations, particularly attainment values, in mediating between their past academic achievement and STEM-related career aspirations. Furthermore, I found that students' endorsement of socio-cultural beliefs such as gender-ability stereotypes in math and science moderated the relationship between students' prior academic achievement and attainment values of math and science tasks. I discuss implications regarding the research findings. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]