<![CDATA[Bullying during early adolescence is a persistent school-health problem associated with emotional distress, impaired school adjustment, and difficulties in peer relationships. Evidence concerning determinants, mental-health consequences, and prevention is distributed across heterogeneous study designs. To synthesise evidence on risk and protective factors, mental-health consequences, and school-based prevention among middle-school or lower-secondary students. This systematic review used narrative synthesis. The final supplementary search was completed on 31 August 2026 using PubMed/MEDLINE, ERIC, PubMed Central, indexed publisher sources, verifiable DOI/Crossref records, and backward and forward citation searching. Reporting was structured according to PRISMA 2020 and PRISMA-S; risk of bias was assessed using RoB 2 and design-specific JBI tools. The included primary studies were published from 2021 to 2026. Eighty-three reports were assessed; 28 were excluded and 55 met the eligibility criteria. After three companion reports were linked with their parent studies, 52 unique studies remained. Family adversity and weak school connectedness were repeatedly associated with bullying involvement, while victimisation was related to depression, anxiety, stress, suicidality, self-harm, and sleep problems. School-based interventions were generally promising, although heterogeneity precluded a single pooled effect. The findings indicate a need for multilevel prevention integrating a supportive school climate, social-emotional competence, family involvement, digital literacy, and meaningful bystander or defender participation.]]>
