Several preliminary studies (Gorard & Smith, 2004; Duru- Bellat, Mons & Suchaut, 2004; Demeuse, Crahay & Monseur, 2001) centring on the question of equality in school systems have highlighted the fact that integrated school systems are globally more egalitarian than differentiated school systems. An "integrated school system" means one that is characterized by a structure common to all pupils over a long period (comprehensive school), a very limited number of optional courses within that common structure, and little or no grade retention. Such school systems are designed to refuse, for as long as possible, to separate pupils on the basis of their performance. In other words, the principle is to allow the school sufficient time to counteract differences in the cultural resources of pupils' families, and to give each pupil real opportunities of success before operating any kind of selection. At the other end of the spectrum, differentiated schooling means the sort of school systems which have subject-routes from a very early stage, employ course channelling and options on a large scale, and make great use of grade retention in managing pupils' progress. In this study the authors start from the observed fact that integrated school systems are globally more egalitarian than differentiated school systems. However, before concluding that curriculum structure has a significant influence on (in)equalities at school, it is important to distinguish between the influence of the socio-economic context underlying each school system, and the specific influence of the structure or organisation of the school system itself. The fact is that not only do the most egalitarian countries with regard to schooling have in common an integrated structure, but also these school systems are set within the context of countries which are more egalitarian in other ways, particularly with regard to income distribution. To distinguish between the influence of this social environment and that of school structure, we offer three analyses based on a secondary analysis of international databases (PISA 2000 and PIRLS 2001, scores in reading literacy) measuring educational attainment in European school systems. Firstly, we test the relationship between an index of income inequality in each country (Gini index) and the level of school inequality of opportunities (measured in this study trough the dependence of the pupils' scores to families' socio-cultural resources). Secondly, we construct a score for every country on the variable "integrated versus differentiated schooling" and we observe the relationship between this score and our index of school inequality. Finally, we observe the deviation between the level of school inequality around ages 9/10 and that observable at age 15. The results of these three analyses lend credence to the hypothesis that inequality of opportunities in school systems has a strong relationship with the school system's structure