According to the analyses of the Swiss 2000 and 2003 PISA data, the composition of students in classes of ninth graders has an influence on their individual achievements. This leads to the question of why it is so difficult to avoid accumulations of students with language and socio-economic disadvantages in certain regions, and their schools. Looking at the processes of social segregation in communities or living quarters brings up theories of social differentiation and choice of residence. Following this theoretical background, relationships between characteristics of community (i.e., tax charge, or living atmosphere), and place of residence of wealthy people, are investigated on a descriptive level. The relationship between the wealth of a community and the level of equipment of their schools is also shown. The theoretical and empirical results make clear that the choice of residence of people with high socio-economic status and the process of social segregation in Swiss schools are interconnected. Multiple stress is also put on foreign-language students from socially disadvantaged milieus who do not live in wealthy communities.