This article explores how the horizontal differentiation of upper secondary education affects students' transitions after graduation. It builds upon the institutional perspective on education and draws on data from a nationally representative survey. The analysis shows a considerable variation in graduates' patterns of transition according to the type of secondary education and that the type of secondary education programme moderates the effect of the academic achievement and of students' socioeconomic background on students' patterns of transition.However, in our view, when studying the influence of horizontal differentiation on young people's pathways, it is necessary to take into account its various dimensions, such as types of institutions, status/prestige of institutions, place of study, programme orientation. Thus, a study carried out within the framework of the eduLIFE project argue for "a more refined concept of upper secondary tracking that distinguishes VET programmes with low and high academic requirements, specialized schools, and baccalaureate schools" (Buchmann et al., 2016).
The present paper addresses the following research questions: How does the horizontal differentiation of upper secondary education affect students' transitions after graduation? andCan the type of secondary education moderate the influence of other factors, for example grades and social background, on those transitions? The present analysis uses Bulgaria as a case study. The Bulgarian system of secondary education provides a fruitful basis for the study of our research question because of its strong internal differentiation, which goes beyond the traditional division into general and vocational education.The paper proceeds as follows. First, we discuss relevant literature and present our theoretical considerations derived from an institutional approach to secondary education. This is followed by a brief overview of the differentiation of Bulgarian upper secondary education and by the formulation of working hypotheses. The data and methods for analysis are described. We proceed with the identification of the patterns of students' transition after upper secondary education. Then, the empirical results are presented. After that, these results are