This study examines spelling development among Korean elementary EFL learners through the Lexical Quality Hypothesis (LQH). A total of 139 students in Grades 4–6 participated in a revised Primary Spelling Inventory. The analyses focused on grade-level differences in spelling accuracy, patterns of feature-level dominance, and the structure of spelling errors, employing type–token ratio and normalized Shannon entropy to measure error diversity and distributional evenness, respectively. The results indicated significant overall improvements in spelling accuracy across grades, although the rate of growth slowed down over time. Feature-level analyses showed that phonological and orthographic features developed concurrently, rather than sequentially, with consonantbased features consistently dominating. In contrast, morpho-orthographic features, particularly inflected endings, exhibited ongoing instability. Error analyses revealed various developmental trajectories, including the expansion and competition of alternative forms, consolidation toward conventional spellings, and instances of reduced variability that suggested premature stabilization of incorrect representations. These findings imply that spelling development is not a straightforward process of error reduction; instead, it is a dynamic process of lexical restructuring characterized by competing representations. The study supports the LQH by illustrating that variability in errors reflects the evolving quality of lexical representations, underscoring the importance of explicit, feature-based spelling instruction in EFL contexts.