While academic achievement is often regarded as positive, emerging research has highlighted high levels of stress among high-achieving pupils. However, it remains unclear whether school-related stress is driven by pupils’ absolute achievement or by their rank within their peer group. The aim of this study was to examine the association between pupils’ achievement rank in class and school-related stress, with a particular focus on gender differences. The study utilised longitudinal survey data from 1691 Swedish pupils, collected in grade 6 (age 13) and grade 9 (age 16), analysed through multilevel and fixed-effects models. There was a positive association between class rank and school-related stress among female pupils, with high-ranking girls exhibiting significantly elevated stress levels also after adjusting for absolute achievement. No association was found among boys. Class rank was not associated with more severe forms of stress or mental health problems. The study suggests that girls may be particularly susceptible to performance pressures and identity formation tied to academic achievement. One interpretation is that there may be a trade-off between short-term stress and long-term educational and labour market success. Schools and educators should acknowledge that high-achieving girls may experience stress despite – or because of – their success.