<p>Interventions focused on adolescents’ identity development have shown promising results, but questions remain as to which adolescents benefit most from them. This preregistered study examined how personality traits (Big Five domains and higher-order meta-traits) moderate adolescents’ responsiveness to the Identity Project, a school-based intervention supporting ethnic-racial identity development. A total of 509 adolescents from 22 classrooms in the southwestern regions of Sweden participated in an intervention and control group design (<i>M</i>_age = 16.28; <i>SD</i>_age = 0.80; 66% female; 51% migration background). Results indicate that extraversion, a personality trait linked to socialization and external reward-seeking, as well as plasticity, a meta-trait linked to adaptability and exploration, both enhanced adolescents’ responsiveness to the intervention in terms of ethnic-racial identity exploration. Moderation differences were found between genders, but not between migration and non-migration backgrounds. With personality traits and meta-traits being revealed as predictors of intervention effectiveness, the study highlights how not all adolescents benefit equally from interventions targeting identity processes. By adapting interventions like the Identity Project to also reach the introverted or less plastic adolescents, it is possible to make them more inclusive, thus broadening their reach and impact.</p>