Spelling performance of Greek–speaking adolescents with developmental dyslexia and co-occurring language difficulties

Abstract This study investigated spelling performance in Greek-speaking adolescents with Developmental Dyslexia (DD–only) and those with Developmental Dyslexia and co-occurring language difficulties (DD+coLD), compared to typically developing (TD) peers, matched on chronological age (CA) and reading age (RA). A total of 98 participants (20 DD–only, 14 DD+coLD, 34 CA, 30 RA) completed measures of fluid reasoning, reading fluency, expressive vocabulary, morphosyntactic skills (production, comprehension), and sentence repetition. A spelling–to–dictation task was also administered, with errors classified into linguistically informed spelling categories. Results revealed distinct spelling profiles for the two dyslexic groups. The DD–only group produced significantly more spelling errors than CA peers, but did not differ significantly from RA peers. In contrast, the DD+coLD group produced significantly more spelling errors overall than both CA and RA peers. Direct comparisons further showed that the DD+coLD group produced significantly more spelling errors than the DD–only group, reflecting differences not only in severity but also in the pattern of errors. These findings demonstrate that co-occurring language difficulties affect spelling performance in adolescence beyond what can be explained by reading level alone and underscore the importance of examining spelling error patterns to distinguish between delayed and more atypical spelling profiles in a transparent yet morphologically rich language such as Greek.