Childhood trauma and non-suicidal self-injury among Chinese students: the mediating role of depression and the moderating role of perceived teacher legitimacy

BackgroundChildhood trauma is a risk factor for non-suicidal self-injury (NSSI), but school-based factors in this pathway remain unclear. This study examined whether depression indirectly linked childhood trauma to NSSI and whether perceived teacher legitimacy moderated the trauma, depression association.MethodsA cross-sectional survey was conducted in 2025 with 576 students from two senior high schools and two universities in northern and southern mainland China. The sample exceeded the minimum size estimated using the standard cross-sectional survey formula, n = Z2p(1 − p)/d2. Childhood trauma, depression, perceived teacher legitimacy, and NSSI were measured using standardized self-report questionnaires. Gender, grade level, and parental educational attainment were controlled. Pearson correlations and PROCESS Model 7 with 5,000 bootstrap resamples were used.ResultsChildhood trauma was positively associated with depression and NSSI. Depression partially mediated the association between childhood trauma and NSSI. Perceived teacher legitimacy moderated the trauma, depression association; unexpectedly, this association was stronger at higher levels of perceived teacher legitimacy.ConclusionDepression may be one important, but not exclusive, pathway linking childhood trauma to NSSI. Perceived teacher legitimacy appears to have context-dependent effects rather than being uniformly protective. These cross-sectional findings support the need for trauma-informed school support, early screening for depression and NSSI risk, and longitudinal research.