Regarding research on inclusive education, it is unknown whether differences in classroom composition provide unequal opportunities for educational outcomes of students with special educational needs (SEN). We investigated effects of student characteristics and classroom composition on reading achievement and social participation of SEN students. Based on a sample of 50 mainstream classes (1,025 Grade 4 students, 137 with SEN) in German primary schools, multilevel analyses showed that SEN students achieved lower in reading and perceived a lower social participation than other classmates. SEN status did not interact with gender, migration background, socioeconomic status, and cognitive ability affecting reading achievement or social participation. There was no evidence of classroom composition effects on the association between SEN status and reading achievement or social participation at the student level: Regarding the observed indicators, we found no significant evidence that inclusive classrooms offer unequal opportunities for learning and social development of primary-school students with SEN.