The choice of the 3 TRA:WELL cooperating schools followed criteria that allow for the best possible scientific comparability while at the same time providing interesting differences as a basis for the analyses. These are (i) similarity in terms of age group (2nd and 3rd grades of lower secondary school, grades 6 and 7 at the start of the project) and school type (general secondary schools), socio-demographic structure of the schools and (ii) differences in terms of location of the residential or school sites (urban: big city vs. small town).