In countries with high differentiation between academic and vocational education, an individual's future prospects are strongly determined by the educational track to which he or she is assigned. This large-scale, cross-sectional study focuses on low-performing students in academic tracks who face being moved to a vocational track. If more is understood about these students, measures could be taken to improve their performance and keep them within academic education. The study investigates performance patterns in academic tracks in the first three years of secondary school in the Netherlands. By identifying patterns that reveal how competence levels in different domains are related at different stages of development and by comparing low performers with other students, the study sheds light on individual and educational aspects that may be amenable to intervention. School grades were analysed for 1596 students. School performance was found to reflect three domains--"languages" (language of schooling and modern foreign languages), "social studies" and "science and math"--that appear to interact in a process of co-construction. General language skills were robustly related to performance in other domains--particularly "social studies"--throughout the first three years of secondary school. By comparison, proficiency specifically in the language of schooling was less strongly related to "social studies" and "science and math" performance after the first year. Suggestions are given as to how educators and curriculum developers could use these insights to accommodate individual and developmental differences and to develop learning materials that may help low performers keep on track.