AbstractWhile both the classroom cultural diversity climate and curriculum-based interventions can promote cultural identity development, they have not been studied together. Drawing on theories of ethnic-racial identity development, the current study aimed to understand the dynamic interplay of a curriculum-based intervention (the Identity Project) with the classroom cultural diversity climate (heritage culture and intercultural learning, critical consciousness socialization and equal treatment) on cultural identity exploration and resolution. Our sample included 906 mid-adolescents in Italy (32.36% immigrant descent, Mage (SD) = 15.12 (0.68) years, 51.73% female), and 504 early adolescents in Germany (53.86% immigrant descent, Mage (SD) = 12.82 (0.89) years, 42.37% female). Bayesian multivariate linear models show that the Identity Project and a stronger critical consciousness climate in the classroom before the intervention promoted cultural identity exploration at post-test in both countries. However, effects of the intervention and facets of the diversity climate on subsequent resolution were only observed in Italy. There was some evidence that the intervention could alter the classroom cultural diversity climate in Germany, while the intervention could compensate for a less positive diversity climate in the slightly older sample in Italy. Thus, it seems promising to systematically build in opportunities to engage with students’ diverse heritage cultures and identities when developing new curricula, as well as to train teachers to implement such curricula.