Across the world, numerous students are being bullied at school. Bullying is often caused by a power imbalance between students. Therefore, identifying potential sources of such a power imbalance can prevent school bullying from happening. Based on the labelling theory, we expect that grade retention can lead to such a power imbalance and, therefore, increase the likelihood of being bullied at school. Hence, this study examines the association between grade retention and self-reported victimisation. We also expect that retainees will be less likely to become a victim of school bullying in schools and countries with a high number of other retainees. If true, this would signal a moderating effect of both school- and country retention composition on the association between grade retention and victimisation. The contextualised impact of grade retention upon victimisation is assessed by cross-national multilevel analyses on PISA2018 data (25 countries; 8,039 schools; 159,412 students). Overall, our findings indicate that being retained in primary and/or secondary education is associated with higher levels of victimisation, while retainees suffer from more victimisation in countries with a low number of other retainees. In contrast to our expectations, however, we did not find such a moderation effect of school retention composition.