Attitudes have gained much attention for supporting the successful implementation of inclusive education. There is evidence that students' attitudes towards joint lessons with students with special educational needs (SEN) affect peer relations in classrooms. But much less is currently known about the relationships between teachers' and students' attitudes and their effects on inclusive processes. This paper draws on social referencing theory to frame how teachers may affect students' attitudes. It postulates that students' attitudes towards peers with SEN and inclusive practices are affected by their teachers' attitudes towards students with SEN and inclusive practices. It also examines how teachers' and students' attitudes relate to classroom climate and social integration. Using a sample of 1.365 German 6th and 7th graders from 64 classes, we run a series of multilevel path models to investigate relationships between teachers' and students' attitudes with social integration and classroom climate. Attitudes are differentiated by a cognitive and affective facet and by whether they relate to students with emotional-social difficulties (SEN-ESD) or learning difficulties. Results show social referencing for cognitive attitudes towards inclusive practices for students with SEN-ESD. Results also indicate that teachers' cognitive attitudes and students' affective attitudes directly affect social integration and classroom climate.