This article reports the main findings from a research phase of the eduLIFE project investigating the role of differentiation in secondary education in producing social inequality in educational opportunities. We conducted a cross-national study involving in-depth quantitatively oriented analyses of the role of educational differentiation in 17 countries characterized by various models of secondary education (the ‘early tracking’, the ‘Nordic inclusive’, the ‘individual choice’ and the ‘mixed tracking’ model). The studies were conducted by reputed scholars in the field who possess expert knowledge of the respective country contexts, and addressed three common research questions: (1) How are pupils sorted into different types of lower and upper secondary education? (2) To which extent do pupils switch between types of secondary education and why? (3) What are the consequences of educational differentiation and sorting in secondary schooling for social inequalities in subsequent educational trajectories? Finally, we describe how these phenomena vary across countries characterized by different secondary educational models. We found that the allocation to different types of secondary education still serves as an important milestone for the intergenerational reproduction of social inequalities in contemporary societies. In all countries, pupils from socioeconomically advantaged families are more likely to attend the types of education that lead to higher achievement and more desirable subsequent educational trajectories. This holds not only in educational systems with formal school tracks but also in those systems in which informal forms of differentiation are prominent.

Keywords: secondary education, social inequalities, educational opportunities, social background, cross-national analysis, longitudinal data