This study uses the Education Longitudinal Survey of 2002 (ELS:2002) to examine how varying levels of intention (planning) and action (choice) in pursuing a science-based major affect American college students' degree attainment in Science and Engineering (S&E) fields by age 26. The study is guided by the Social Cognitive Career Theory's performance model that is appropriate to examine educational attainment. A key element of the theory consists in personal goals to engage in STEM education in college. In this paper, we view students' intention to pursue specific college majors and/or actual action to enrol in a specific major as an expression of aspirational goals associated with degree attainment, so closer the intention-action gap, more likely to attain the goal. The proposed aspiring-scientist typology appears to be the main determinant of S&E degree attainment by age 26, when controlling for socio-demographic, pre-college, and postsecondary factors. Students with high level of science aspirations have greater chance to complete an S&E degree. Medium-aspiration students are more likely to complete non-S&E degrees, after starting in science-based majors. Low-aspiration students are more likely to attain certificate/associate degrees in any field or be non-completers.