Internalizing problems rise during adolescence, yet the stable underlying dimensions remain unclear. Using two longitudinal samples (Sample A: \(N = 488\) , 43% girls at birth, adopted children, ages 7–16; Sample B: \(N = 222\) , 50% girls at birth, biological children from low-income families, ages 7–17), we examined dimensions of internalizing symptoms (excluding somatic complaints) on the Child Behavior Checklist using exploratory structural equation modeling (ESEM) and confirmatory factor analyses. In Sample A, three dimensions emerged: low self-worth/depression (LSW/Dep), social/general anxiety (S/GA), and depression/withdrawal (Dep/With). In Sample B, S/GA and Dep/With combined into the social anxiety/withdrawal (SA/With) factor, alongside LSW. Both solutions were largely stable across age and sex. Factor trajectory analyses revealed that levels of all dimensions increased from childhood to early adolescence, for both sexes. Trajectories subsequently diverged: LSW/Dep became more pronounced in girls only, S/GA increased in girls and declined in boys, and Dep/With showed the steepest increase for both sexes. Dimensions showed strong homotypic but weak heterotypic continuity. Findings highlight distinct developmental and sex-specific pathways of internalizing vulnerability detectable in middle childhood, supporting earlier and more targeted identification and intervention.
