# Developmental Change in Associations Between Mental Health and Academic Ability Across Grades in Adolescence: Evidence from IRT-Based Vertical Scaling

## TL;DR

This study shows that better vocabulary skills in middle school are linked to lower anxiety and depression, with the strongest effect in Grade 8.

## Contribution

The study introduces IRT-based vertical scaling to track academic and mental health links across adolescence.

## Key findings

- Higher vocabulary ability is associated with lower depression, anxiety, and stress in middle school.
- The strongest mental health benefit of vocabulary ability occurs in Grade 8.
- IRT-based vertical scaling effectively tracks academic and psychological development across grades.

## Abstract

Adolescence is a critical period when rapid cognitive maturation coincides with heightened emotional vulnerability. This study examined the dynamic association between academic ability and mental health across early adolescence, focusing on vocabulary ability as a core indicator of academic ability. Using large-scale data from Grades 1–12 (N = 13,412), a vertically scaled vocabulary ability scale was constructed based on Item Response Theory (IRT) and the Non-Equivalent Anchor Test (NEAT) design to achieve cross-grade comparability. Fixed-parameter calibration was then applied to an independent cross-sectional sample of middle school students (Grades 7–9, N = 401) in Tianjin, combined with the DASS-21 to assess internalizing symptoms (depression, anxiety, stress). Hierarchical multiple regression analyses revealed that higher vocabulary ability was significantly associated with lower levels of depression, anxiety, and stress, with the negative association strongest in Grade 8. The present study provides new empirical evidence for understanding the interactive mechanisms between academic and psychological development during adolescence. Methodologically, the study demonstrates the value of IRT-based vertical scaling in establishing developmentally interpretable metrics for educational and psychological assessment.