School leavers with low educational attainment face great difficulties in their school-to-work transitions. They are, however, quite heterogeneous in terms of their personal and social resources. These within-group differences may influence who shows initiative during the school-to-work transition period and thereby helps employers recognize their learning potential at labor market entry. Yet this recognition also depends on the ways employers select applicants, which may prevent them from discovering such within-group differences. We therefore investigate the interplay between agency and its constraints, that is, whether higher cognitive and noncognitive skills and more parental resources provide low-achieving school leavers with new opportunities in the school-to-work transition period or whether their low school attainment causes the persistency of their disadvantages. We use panel data from the German National Educational Panel Study (NEPS), which started in grade 9. The NEPS also includes school leavers from special-needs schools. Our sample consists of 3417 low-achieving adolescents (42% female), defined as adolescents who leave school with no or only a lower secondary school-leaving certificate. Their average school-leaving age is 16 to 17 years. Our key findings are that the transition period opens up new opportunities only for those low-achieving adolescents with better vocational orientation and higher career aspirations, leading them to make stronger application efforts. The success of youth’s initiative varies considerably by school-leaving certificate and school type but not by competences, noncognitive characteristics, and parental background. Thus, the label of “having low qualifications” is a major obstacle in this transition period—especially for the least educated subgroup. Their poor school attainment strongly disadvantages them when accessing the required training to become economically independent and hence in their general transition to adulthood. Our results are also of interest internationally, because participation in firm-based training programs functions as the entry labor market in Germany. Thus, similar explanations may apply to low-achieving adolescents’ difficulties in finding a job.