<p>Paradoxically, very low-bullying school environments may exacerbate the psychological distress of victimized students, a phenomenon known as the “healthy context paradox.” While prior research has confirmed this paradox for internalizing problems, evidence regarding externalizing problems and its underlying mechanisms remains limited. Guided by the individual–group similarity model and social information processing theory, this study examined whether classroom-level victimization moderates the association between individual victimization and externalizing problems, and whether negative peer beliefs mediate this association. Surveying 1,491 fifth- and sixth-grade students from 30 classes in China, results showed that low classroom-level victimization amplified externalizing problems through negative peer beliefs, revealing a novel mediating mechanism in this paradox.</p>