<p>This population-based study examined the trends in psychosocial wellbeing among Finnish adolescents attending the 8th and 9th grades of middle school from 2017 to 2023, comparing majority-population and immigrant-origin adolescents. Using repeated cross-sectional survey data (<i>N</i> = 285,354), we also investigated whether associations between demographic, school-related factors, and psychosocial wellbeing changed over time across groups. Overall, psychosocial wellbeing declined during the study period. However, subgroup analyses revealed distinct patterns, including gradual change and relative stability. Notably, in 2023 females with forced immigrant backgrounds reported better psychosocial wellbeing compared to female peers in other groups, including the majority population. Associations between demographic factors and wellbeing were mostly stable, except those adolescents who had resided in Finland for less than a year reported better psychosocial wellbeing in 2023 compared with earlier cohorts. Overall, the associations of school difficulties and classroom social climate with psychosocial wellbeing strengthened over the years, while teacher support remained relatively stable. However, subgroup analyses revealed some unique changes in these links across immigrant groups. Strikingly, in 2017 the associations of school difficulties and classroom social climate were equal among majority-population and most immigrant-origin adolescents, while in 2023 the associations of these factors were weaker among most immigrant-origin adolescents relative to the majority population. Fortunately, while considerable differences in previous years were observed regarding the link of teacher support and psychosocial wellbeing, in 2023 the links among majority- and immigrant-origin adolescents were equal. Findings highlight the evolving role of schools in adolescent psychosocial wellbeing and the need for targeted support.</p>