Although schools have been described as an important socialization context for the development of intergroup attitudes, longitudinal multilevel studies are still rare within this field. This 3-wave study (with annual assessments) of German adolescents (N = 1292; Mage = 13.86; 51.8% female) examined the role of school experiences (perceived multicultural education, supportive peer relations in class, democratic classroom climate) in the development of youth's negative attitudes toward immigrants. Longitudinal multilevel analyses revealed that a democratic classroom climate predicted youth's attitudes at the individual level. At the classroom level class-average perceptions of a democratic classroom climate, supportive peer relations in class, and multicultural education (the latter solely among male, higher track students) were associated with less negative attitudes toward immigrants. In addition, age moderated the effect of school experiences on attitudes, showing that perceptions of a democratic climate at the classroom level mattered in particular among older adolescents. The findings suggest that school experiences are related to youth's negative attitudes toward immigrants and can therefore help to reduce the risk of prejudice development.