Beyond Global IQ: Identifying Subgroups of Intellectual Functioning in Dyslexia Through Latent Profile Analysis.

Dyslexia, a heterogeneous neurodevelopmental disorder, is characterized by persistent reading and spelling difficulties despite average intellectual potential. Although intellectual functioning in dyslexia is often described as average, emerging evidence suggests meaningful within-group variability. This study examined whether children and adolescents with dyslexia exhibited distinct intellectual profiles based on the Stanford-Binet Intelligence Scales, Fifth Edition (SB5). Data were obtained from a large, diagnostically verified sample of 3458 individuals aged 10-19 years assessed in psychological-pedagogical counseling centers across Poland. We used latent profile analysis (LPA) of all 10 SB5 subtests and compared models that specified 2-6 latent classes. The optimal solution identified two profiles: (a) a small subgroup (5%) with globally reduced intellectual functioning and a profound deficit in verbal working memory (>3 standard deviations below the norm) and (b) the predominant subgroup (95%) with broadly average intellectual functioning and relatively preserved reasoning abilities. Profile membership was associated with socioeconomic status; the low-functioning subgroup was associated with lower parental education and age, as younger participants were more likely to belong to this group. These findings highlight the dimensional nature of intellectual heterogeneity in dyslexia and underscore the diagnostic value of profile-based approaches over global intelligence quotient (IQ) scores.