This paper examines how an adolescent's relative socioeconomic status (SES) within their school influences their socioemotional development and well-being. Although peer effects on academic outcomes are well-documented, less is known about how an individual's socioeconomic rank among peers shapes non-cognitive skills. Using PISA 2022 data and a school fixed effects model, we investigate the relationship between two measures of relative SES—Socioeconomic Rank and Socioeconomic Gap—and a range of outcomes, including socioemotional skills, self-esteem, and attitudes toward school. Our results show that higher within-school SES rank is significantly associated with better socioemotional skills, greater well-being, and stronger academic motivation. We also find important heterogeneity by gender and migrant background. These findings highlight that an individual's relative socioeconomic position, beyond absolute resources, plays a critical role in shaping adolescent non-cognitive development.