Comparative analyses of the Programme for International Student Assessment between immigrant and native students place immigrant students in an unfavourable position in schools, with disadvantageous indicators regarding socioeconomic and professional paths. However, the Programme for International Student Assessment assesses a series of dimensions that involve constructs that have been little studied in the school immigrant population and that relate to self-concept and school adjustment. Based on the Programme for International Student Assessment's most recent edition, Portugal's database of 7,325 15-year-old students was analysed. We selected 438 immigrant cases with two objectives: (1) to evaluate the impact of the length of exposure in the host country on three dependent variables of school adjustment: sense of belonging, perceived loneliness and attitudes towards school (expectations of educational and professional opportunities); (2) to evaluate the differences in results for the same dependent variables, but considering the first and second generation of immigrants in Portugal. For the data analysis, sampling weights and plausible values were analysed with the International Database Analyzer. The results show that students who have been in the country for a year or less have greater difficulties and increased significant differences compared to other migrant groups in the referred indices of self-concept and inclusion. However, other groups, especially those with periods of long-term residence between four and five years, also face substantial levels of school maladjustment.