Reading and Writing Abilities in Students with Mild Nonspecific Intellectual Disability: A Multivariate Examination of Literacy and Cognitive Processing Abilities

Individuals with mild nonspecific intellectual disability (NSID) often exhibit delayed literacy development. Unfortunately, how cognitive-linguistic processing profiles influence literacy in this population lacks clarity. This study investigated literacy development in this population, considering the cognitive-linguistic mechanisms. The Specialist Battery for the Diagnosis of Cognitive Abilities and School Skills was used to assess cognitive-linguistic abilities and literacy-related skills in 122 participants. Fuzzy C-means clustering was used to identify processing profiles. Developmental age equivalents in literacy were estimated using local regression models and matched comparisons with typically developing peers. Two cognitive-linguistic profiles emerged: globally weaker and moderately developed. Those with NSID performed significantly lower than their peers in all domains. Their literacy skills aligned with those of children 2-4 years younger, and plateaued after age 15. Cognitive-linguistic heterogeneity in students with NSID should guide targeted literacy interventions. The findings inform ICD-11 educational expectations for individuals with mild NSID.