In this article, we use high-quality register data from Finland as a case study, to test the segmented assimilation hypothesis on school performance of immigrants by generation, including children of exogamous families; and if generational differences in school performance are explained by the stage at which the child immigrated in the receiving country. Preliminary results show a generational gradient of school performance, with 1^st generation immigrants having grade point averages lower than natives and of other immigrant generations. The same pattern is observed for enrollment in education at ages 18-20. Educational level of parents is strongly associated with school performance, and explains a large part of the generational gradient. Next steps include the inclusion of: the life stage when the immigration of the child occurred; age of the biological mother at the time of child; divorce of the parents earlier in childhood; a contextual measure indicating the attended school.