In the course of the achievement study ,Competencies And Attitudes Of 7th Graders (KESS 7)' conducted in the City of Hamburg, information about the pupils' social backgrounds - similar to PISA or PIRLS - was gathered. The operationalisation of relevant criteria was carried out on basis of Bourdieu's (1983) and Coleman's (1996) theoretical work. The aim was to create an index for assessing the economic, social and familial resources of pupils from different schools (cp. Bos et al. 2006).On basis of individual data about the pupils' socio-economic background schools were classified ,disadvantaged' or ,privileged' referring to the school specific composition of pupils. The analysis of the KESS-7-data shows that the three forms of capital (economic, cultural and social) that are incorporated into the index can be attributed to a combined construct consistently with theory. In fact the three forms of capital can be attributed to distinctive factors, yet a general factor model can be computed without loss of information as well. In the course of the development and improvement, the index was computed using the benefits of the Rasch-Model. The analysis clarifies the specific benefit of using indicators for all three forms of capital in contrast to only one economic measure. Whereas the indicators for economic capital are all located in the middle segment of Rasch-distribution, the indicators for cultural capital are useful for a differentiation in the upper segment of the scale's continuum. However, for a differentiation in the lower segment indicators for social capital are required. The index can be used as a means for adequate and fair comparisons of the effectiveness of different schools. Whether the social index which was developed for use in an urban agglomeration (Hamburg) also can be implemented in rural areas with different characteristics is analysed within the scope of ongoing research. Bos, W., Pietsch, M., Gröhlich, C. & Janke, N. (2006). Ein Belastungsindex für Schulen als Grundlage der Ressourcenzuweisung am Beispiel von KESS 4. In Holtappels, H.G., Bos, W., Pfeiffer, H., Rolff, H.-G. & Schulz-Zander, R. (Hrsg.), Jahrbuch der Schulentwicklung. Band 14. Weinheim: Juventa. Bourdieu, P. (1983). Ökonomisches Kapital, kulturelles Kapital, soziales Kapital. In R. Kreckel (Hrsg.), Soziale Ungleichheiten (S. 183-198) (Soziale Welt, Sonderband 2). Göttingen: Schwartz. Colemann, J. S. (1996). Der Verlust sozialen Kapitals und seine Auswirkungen auf die Schule. In Leschinsky, A, (Hrsg.), Die Institutionalisierung von Lehren und Lernen.( S. 99-105) Weinheim: Beltz (Zeitschrift für Pädagogik, 34. Beiheft).