This study examines how acceptance of violent behavior translates into school violence involvement among lower secondary students in Hue, Vietnam, and whether this relationship is conditioned by peer-group context. Drawing on survey data collected in 2024 from three schools, the analysis moves beyond a simple norm-behavior framework to conceptualise acceptance as subjective legitimation embedded in social environments. Results show that acceptance is positively associated with involvement in all three forms of violence, with the strongest effects observed for psychological/relational aggression and weaker associations for cyber violence. Interaction models further indicate that the acceptance-behavior link becomes stronger when students perceive their peer group as more violence-prone, suggesting a process of contextual amplification. However, the moderating effect modestly increases overall explanatory power, indicating that peer-group context conditions rather than replaces individual acceptance. The findings highlight that the translation of tolerant attitudes into behavior does not occur in isolation but unfolds within proximate peer dynamics. Effective prevention strategies should therefore address both attitudinal legitimation and the peer-group environments in which violent practices are reinforced.