Adolescents need to develop career preparedness to successfully transition from school to work. Many factors represent career preparedness, which are difficult to measure comprehensively and economically. We used a career resources framework to assess key aspects of career preparedness among in-school adolescents, and adapted and validated the Career Resources Questionnaire. The questionnaire assesses 12 distinct aspects of career preparedness (i.e., occupational expertise, labor market knowledge, soft skills, career involvement, career confidence, career clarity, social support from school, family, and friends, networking, career exploration, and self-exploration). We demonstrate the reliability, factor structure, and validity evidences based on internal structure and relations with other variables of the new measure among two samples (N1 = 186; N2 = 1,004). In sum, the study indicates that the assessment can be used by researchers and practitioners to reliably and economically assess several key indicators of career preparedness.