The PIRLS and PISA studies on student performance have shown that social inequalities in Germany intensify between the end of primary education and the end of lower secondary education. The question arises at which stage of the educational career the high social inequality in Germany arises and what are its determinants. These are the main goals of the project. One focus of the study is whether social inequalities in educational achievement originate from the allocation of students into the different secondary school types or if they arise within secondary schools.