Pupils who did not start learning at the same level as their peers might subsequently fall behind throughout their educational careers (e.g., Heckman 2006; Passaretta et al. 2022). The modalities of compulsory school admission may contribute to the emergence of early gaps in educational performance. Nearly all education systems have arbitrarily chosen cut-off dates for school enrolment, which create age differences of up to a year within a cohort of pupils. Prior research has shown that the youngest pupils in a cohort fall behind their relatively older peers in educational performance (e.g., Bedard and Dhuey 2006; Peña 2017; Dicks and Lancee 2018). These performance gaps are coined as relative age effects, which can be framed within theories of cumulative (dis)advantages (e.g., DiPrete and Eirich 2006). Drawing on a comprehensive data set encompassing the entire student population in North Western Switzerland (BR NWCH 2021), the study addresses three research questions. First, it is investigated to what extent pupils’ relative age affects their educational achievement in different subjects and track placement in secondary education. Second, by exploiting the longitudinal structure of the data, it is examined whether the influence of relative age diminishes the course of educational trajectories. Third, the study establishes a record linkage between administrative data and pupils’ test data to investigate whether pupils from disadvantaged backgrounds suffer more strongly from relative age effects. A pupil’s relative age might be correlated with various unobserved factors. Two strategies are employed to address these endogeneity concerns. First, the study employs an instrumental variable approach using “assigned relative age” (e.g., Bedard and Dhuey 2006) as an instrument for pupils’ actual age. Second, the study uses a regression discontinuity design contrasting pupils born just before and after the cut-off date to estimate relative age effects in Switzerland. Preliminary results provide evidence that students with a relative age advantage when they entered school achieve significantly higher than their counterparts with a relative age disadvantage during their first years of primary education. However, relative age effects vanish the more students advance in their educational trajectory. Additional analyses shed light on potential effect heterogeneity. The study illustrates how early disadvantages emerge by chance through arbitrarily chosen cut-off dates for school eligibility. Scholars and policy-makers alike are urged to debate how the modalities of school entry can be designed to ensure equal starting conditions for all.

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