Purpose: Regarded as an important means of career development, preparation, and transition, career adaptability is a lifelong skill that can enable individuals to overcome 21st-century work--life requirements and challenges. This study aims to investigate the factors contributing career adaptability of high-school students, which pose beneficial implications for career counseling research and practice. Research Methods: The sample comprised 1,610 students from public (n = 862) and private (n = 748) high schools in Ankara, Turkey. The Multidimensional Perceived Social Support Scale, Life Orientation Test-Revised, General Self-Efficacy Scale, and Career Adapt- Abilities Scale served as data collection instruments. Multisample structural equation modeling (SEM) was used to investigate model differences across school type. By the reason of model invariance, single-group SEM was used to examine the model on the entire dataset. Findings: Results indicated that the measurement model fit with the data, while results of multigroup confirmatory factor analysis confirmed measurement equivalence under the assumptions of configural and metric invariance. Results showed that the hypothesized model accounted for 46% of the variance in career adaptability and thus corroborated the effects of perceived social support and optimism in predicting career adaptability via general self-efficacy. Implications for Research and Practice: Findings highlight the role of general self-efficacy, optimism, and social support in high-school students' career adaptability. There is a need for a carefully planned guidance and career education program, beginning in the elementary grades and continuing through secondary school. [This paper was presented at the Third International Eurasian Educational Research Congress.]