The present study examined the direction of effects between peer likeability and youth's school adjustment and psychological well-being, and the moderation of these effects by students' immigrant status. One thousand one hundred and eighteen students (63% immigrants) nested in 57 Greek middle-school classrooms took part in the study (Wave 1; age M = 12.6 years). Data were collected from multiple sources and informants. The results reveal complex, in some cases bidirectional effects over time between peer likeability and different indices of school adjustment and psychological well-being. Being liked by Greek, but not by immigrant, classmates influenced students' well-being over time. In contrast, being liked by either immigrant or Greek classmates predicted changes in students' school adjustment. The results highlight the importance of supporting positive peer relations among youth in order to promote other adaptation outcomes. In the case of immigrant youth, they suggest that interventions need to promote positive intergroup contact between them and their nonimmigrant classmates in order to support their well-being.