Low academic achievement has been shown to lead to higher disengagement from school, the main acculturative arena for immigrant-origin youth. Therefore, we tested the hypothesis that their disengagement from school will lead over time to lower involvement with the national culture and higher involvement with the ethnic culture. To test this hypothesis, we examined developmental cascades linking academic achievement to school engagement and spreading to national and ethnic acculturation, in a three-wave longitudinal study of immigrant adolescents in Greece. Cross-lagged analyses revealed that lower academic achievement cascaded over time to decreases in school engagement, which in turn cascaded to decreases in national, and increases in ethnic, involvement. School engagement fully longitudinally mediated the effects of academic achievement on both national and ethnic involvement. All cross-lagged effects in the reverse direction were non-significant. The results highlight the importance of schools in immigrant-origin youth’s involvement with the national culture.