Firmino, JoãoNunes, Luís Catelade Almeida, SílviaBatista, Susana2026-03-022026-03-0220261558-2159PURE: 116177160PURE UUID: c4ca5a38-3be8-4ec6-b31e-2738e59f9367Scopus: 105004065067ORCID: /0000-0001-8115-6223/work/207209382ORCID: /0000-0003-2545-4538/work/207209475http://hdl.handle.net/10362/200808Publisher Copyright: © 2025 Taylor & Francis Group, LLC.We examine segregation of low-achieving, immigrant, and low-socioeconomic status students (grades 1–12), across 5,000 Portuguese public schools in all 278 mainland municipalities, over a decade (2006/07-2016/17). The density-corrected dissimilarity index is used to assess school-segregation within municipalities and class-segregation within schools, the latter a segregation dimension under-explored in the literature. School-segregation was mild and stable but higher in primary education, reflecting small school-catchment-areas and residential patterns. Class-segregation was similarly mild and stable, though more pronounced in upper-secondary education–especially for low-achievers–likely due to academic tracking. The study highlights how school choice and tracking shape segregation patterns.172982766engclassimmigrantlow-achieverschoolsegregationSESEducationjournal article10.1080/15582159.2025.2491844https://www.scopus.com/pages/publications/105004065067