This study investigated how schools can contribute to students’ generalized social trust (GST). Positive social experiences with trust and the experience of being part of a fair and predictable social system are important sources of trust. Students’ sense of school membership (SSM) reflects these sources. We investigated the association between three aspects of SSM and GST in 9th grade of Dutch secondary schools (78 schools, 230 classrooms, 5167 students). The diversity of the school population, in terms of track and ethnicity, was included as a moderator. All three aspects of SSM appeared to be positively associated with GST. School ethnic diversity strengthened the association between ‘identification and participation’ and GST but weakened the association between ‘peer acceptance’ and GST. This creates an impetus to support all students to experience a sense of school membership and raises the question how students can profit more from the diversity of the school community.