The Mediating Role of Vocabulary in Linking L1 Reading and L2 Proficiency

Abstract

This study examined how first language (L1) reading relates to second language (L2) proficiency and whether L2 vocabulary mediates that relationship in a Japanese university context. Participants were 213 first-year students at a private university. L1 reading was assessed with the Reading Skills Test (RST), L2 vocabulary with the New General Service List Test (NGSLT), and L2 proficiency with the TOEFL ITP sections of Listening, Structure and Written Expression, and Reading. A structural equation model estimated both direct and indirect paths among the three constructs. Results showed a positive effect of L1 reading on L2 vocabulary (β = .28, p .05), indicating full mediation through vocabulary. Measurement limitations, including weak factor loadings for some TOEFL subtests (λ = .49-.64), warrant cautious interpretation. The findings highlight vocabulary as the primary channel through which L1 literacy advantages influence the placement-oriented proficiency measures used here. Pedagogically, sustained vocabulary instruction and continued support for L1 reading appear essential. Future research should broaden the definition of proficiency to include productive skills and adopt a longitudinal design to test whether vocabulary growth precedes later gains in overall proficiency.

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