Germany historically responded to student diversity by tracking students into different schools beginning with grade 5. In the last decades, sociopolitical changes, such as an increase in "German-as-a-second-language" speaking students (GSL), have increased diversity in all tracks and have forced schools to consider forms of individualization. This has opened up the scientific debate in Germany on merits and limitations of individualization for different student groups within a tracked system and heterogeneous classes. The aim of the present exploratory study was to examine how individualized teaching (i.e., teacher self-reported individualized teaching practices and individual reference norm orientation) is related to student-perceived teaching quality. Additionally, we considered moderation effects of classroom composition in relation to achievement and proportion of GSL students. Longitudinal data came from 35 mathematics classes with 659 9th and 10th grade students. Results showed significant relation between teacher self-reported individualized teaching practices and individual reference norm orientation and monitoring. Regarding the composition effects, the proportion of GSL students in class moderated the relation between teacher self-reported individual reference norm orientation and cognitive activation. Our findings contribute to the growing body of evidence that classroom composition can differentially impact the relation between teachers' behaviors and students' perceptions of teaching quality.