Previous studies do not allow us to obtain an overview of between-school segregation in Spain. This new study estimates the magnitude of school segregation by socioeconomic level in Spain and its Autonomous Communities, and compares these results with other countries of the European Union. To achieve our aim, we conduct a special exploitation of the PISA-2015 dataset. The Spanish sample consists of 39,066 students from 1,177 schools. In addition, data from 27 of the 28 countries of the European Union were analyzed, excepting Cyprus that did not participate in PISA-2015. The total sample for this study is 208,873 students and 7,553 schools. We use the ESCS –Index of economic, social and cultural status– as created by PISA - to estimate school segregation by socioeconomic level using two of the most important segregation indices: the Gorard unevenness index and the Isolation index. In order to calculate both indices, we will consider four criteria for the selection of the minority group: • 10% and 25% of students with families with lower socioeconomic and cultural level • 10% and 25% 25% of students with families with higher socioeconomic and cultural level, We also estimate the average of both indexes for comparable purposes. For the calculation of both indices, the final weights of each student, provided in the PISA-2015 database for each country, have been taken into account. Results indicate that the average segregation is Spain in its unevenness dimension is 0.38 (Gorard index) and 0.32 in its exposure dimension (Isolation index). This indicates that Spain is one of the most segregated countries in Europe, similar to those in the East that are more segregated (such as Bulgaria, Slovakia, Romania), and worse than the countries in their closest context (France, Italy, UK). School segregation in the Autonomous Communities offers extreme results, some of which are among the lowest in Europe (Illes Balears, Galicia and Aragon) and others such as the Community of Madrid with very high segregation, only surpassed by Hungary within the European Union. The paper explores the reasons for these results, and considers why the situation in Spain is so unlike that of its neighbours. Our findings highlight the impact of regional educational policies on the admission criteria to schools, showing that policies such as the promotion of private education, assessing the competence of schools through the publication of rankings, or even the creation of a single district can set up unequal educational systems.

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