The aims of this study were to gain insight into the quality of inclusion in mainstream classrooms involving students with Down syndrome and to reveal underlying predictors. A total of 39 8-year-olds with Down syndrome and their teachers participated. Via a survey, the teachers were asked to rate key indicators of inclusion. Their average rating corresponded to a moderate quality of inclusion, suggesting that the students with Down syndrome participated as active and accepted class members who learned with their peers. At the same time, the academic instruction of the students tended to take place outside the mainstream classroom. Regression analysis showed that teacher collaboration and the children's expressive language abilities explained a reliable portion of the variation in the quality of inclusion. The implications for understanding and facilitating inclusion in practice are discussed.