Identifying Defender Subgroups and Their Classroom Distribution Patterns in Chinese Adolescents: A Social-Ecological Multilevel Latent Profile Analysis.

Defenders are critical in preventing school bullying, yet the association of their heterogeneity with social-ecological factors remains underexplored, especially over long-term development. Using a multilevel framework, this longitudinal study examined subgroups of defenders among Chinese adolescents, their distribution patterns at the classroom level, and how social-ecological factors influence these subgroups. Data were collected from 3569 junior high school students (initial M_age = 12.69 ± 0.49, 47.5% girls) across 76 classrooms in three waves at half-year intervals. Multilevel latent profile analysis identified six defender subgroups (frequent aggressive, frequent nonaggressive, moderate aggressive, moderate nonaggressive, infrequent, and nondefenders) and two classroom patterns (high- and low-defending). From the first to the second semester of eighth grade, nonaggressive defenders generally decreased, while aggressive, infrequent, and nondefenders increased at both the student and classroom levels. Furthermore, social status, classroom status hierarchy, and classroom bullying norms predicted defender subgroups, with effects that varied over time. These findings emphasize the necessity of considering defender heterogeneity from a social-ecological perspective and offer insights for classroom-level interventions.