Nowadays, an increasing number of children and adolescents living in Europe have an immigrant background. Because ethnicity is a recognizable characteristic that may become the driver of bullying, these youths are at high risk of victimization. School interventions based on peer-led approaches, assuming all the conditions postulated in contact theory, could be suitable to counteract bias-based bullying and victimization. This study aims to analyze whether the NoTrap! antibullying program, an evidence-based peer-led intervention, may also be effective in counteracting ethnic bullying and victimization when students with an immigrant background are involved as peer educators. There were 1,570 students who participated in the study: 24 control classes (N = 476) and 50 experimental classes (N = 1094). Within the last group we identified two conditions: 30 classes in which all peer educators were Italian (Experimental A, N = 661); 20 classes in which at least one of them had an immigrant background (Experimental B, N = 433). Results of two linear mixed models showed a significant interaction Time 3 Experimental condition for ethnic victimization, F(1, 1170) = 4.185; p = 0.015. Specifically, the NoTrap! is effective in reducing ethnic victimization when at least one student with an immigrant background is involved as a peer educator. Only in this condition, indeed, peer educators are directly involved in the phenomenon they counteract, and all four circumstances postulated in the contact theory are satisfied. No effects on ethnic bullying have been found, F(1, 1162) = 0.215; p = 0.806. This is in line with the activities proposed in the program, which is more focused on empowering victims than on acting directly on bullies.