More attention is needed on the career development of adolescents, specifically disadvantaged students deemed at risk of school failure. We investigated the determinants on career development competencies of 9th graders in secondary school in South Korea. The data in this study included 394 principals, 6635 students, and the students' parents. Our research confirmed that students with low academic achievement, less parental support, and low family income are relatively disadvantaged in their school-based career development. We suggest that schools provide more preferential attention and care, as well as special career interventions for these disadvantaged students.