Background: Differences in competence gains between academic and non-academic track schools are often attributed to selection effects based on students' primary school performance and socioeconomic status (SES). However, how the competencies of comparable students (in terms of school performance and social background) at different tracks develop is often neglected. Aims: We investigated whether comparable students diverge in their math competencies due to attending different types of secondary schools, contributing to the ongoing debate on whether inaccurate stratification may lead to disadvantages. Methods: Using data from the National Education Panel Study (Kindergarten Cohort SC2, N = 4180), we examined students' competence development from the fourth to seventh grade. We employed a quasi-experimental design (propensity score weighting, PSW) comparing similarly capable students at academic and non-academic school tracks to make causal inferences. The outcome variable was students' math competence in seventh grade. PSW used fourth-grade competency measures in math and reading and other variables such as sex, migration background, SES, class composition, special educational needs, school grades and school location. Results: Results revealed a significant average treatment effect on the treated, indicating that comparable students attending non-academic track schools show lower math performance than those at academic track schools. Conclusion: Non-academic tracks seem to hinder the full development of students' competencies. We conclude that the effects of preconditions like the students' SES, ability and aspirations on competence development are lower than assumed and that school learning environments should be given greater importance. We discuss practical solutions and provide suggestions for future research.