Yan Zhang

Background and Purpose: Non-suicidal self-injury (NSSI) is a global concern in adolescent mental health. Rural boarding middle school students, as a unique and vulnerable population, remain understudied regarding the potential heterogeneity and longitudinal trajectories of NSSI. This study aimed to identify latent classes of NSSI among this group, examine their transition patterns over time, and evaluate the effectiveness of an emotion management group intervention. Methods: Study 1 cross-sectionally surveyed 927 adolescents; we split samples into non-NSSI and NSSI subgroups and ran latent profile analysis (LPA) only among participants with NSSI ( n =285). Study 2 conducted a 6-month follow-up of 550 participants and applied latent transition analysis (LTA) to examine class shifts and predictive factors. Study 3 was a randomized controlled trial in which 30 students from the High-NSSI received an 8-week emotion-management group intervention. Intervention effects were evaluated using repeated-measures ANCOVA with demographic covariates. Results: Within the NSSI subgroup ( n = 285), two classes were identified: a High-NSSI class ( n = 21, 7.4%) and a Low-NSSI class ( n = 264, 92.6%). Poor sleep quality and bullying victimization independently predicted High-NSSI membership. Longitudinal analysis revealed high stability in the Low-NSSI class (91%) and high fluidity in the High-NSSI class (83% transitioning to low-risk). The emotion-management intervention significantly reduced both NSSI frequency and negative affect. Discussion: These findings demonstrate that clinically meaningful NSSI subtypes exist among rural boarding adolescents and that sleep quality and bullying are key modifiable risk factors. The results support a stepped-care approach in school settings, where the High-NSSI class requires intensive intervention and the Low-NSSI class may benefit from less intensive, universal supports. The emotion-management group intervention is an effective school-based program for the most severe NSSI subtype. Keywords: non-suicidal self-injury, latent profile analysis, latent transition analysis, emotion management, group intervention