We provide the most comprehensive description of student segregation in the Portuguese public school system to date, a system that exhibits interesting institutional features potentially linked with the student segregation issue (e.g. school catchment areas, course tracking, and almost no central regulations regarding class composition). The analysis uses the entire regular student population enrolled in all public schools of continental Portugal (grades 1 to 12, from 2006/07 to 2016/17). Looking at three segregation dimensions – economic, academic, and immigrant – at both between and within-school levels, and using a novel dissimilarity index recently proposed in the literature aimed at better capturing systematic segregation, we find that segregation, on median, is mild, across time, grades, and regions. The most important exception is the case of within-school academic segregation. During upper-secondary schooling, in particular, when students are divided across classes according to own course-tracking decisions, it doubles. Moreover, within-school academic segregation estimates have the largest interquartile ranges, within a given year, grade, or region, pointing to heterogeneity in the way different schools set up classes internally in terms of students' academic characteristics. Academic and economic segregation are positively associated, at both between and within school levels. The Portuguese segregation insights are also compared to those from other geographies
