Symbolic and non-symbolic geometric abilities across development and in individuals with dyscalculia and dyslexia

Geometry is fundamental to mathematical thinking, yet its foundations and difficulties in learning disorders remain poorly understood. Here, we investigated the development of geometric abilities and their relationship with developmental dyscalculia and dyslexia. Seventy-nine children and adults, including individuals with and without learning difficulties, completed behavioral measures of non-symbolic geometry and a paper-and-pencil assessment of symbolic geometry. Geometric abilities continued to develop from early adolescence into young adulthood and non-symbolic geometry predicted symbolic geometry independently of age, verbal reasoning, non-verbal reasoning and visuospatial working memory. Adults with dyscalculia, most of whom also had dyslexia, showed impairments in both non-symbolic and symbolic geometry that persisted after controlling for visuospatial working memory, whereas individuals with dyslexia without dyscalculia performed comparably to controls. These findings suggest that non-symbolic geometry contributes to formal geometric competence and that geometric difficulties may be a persistent feature of developmental dyscalculia, with implications for education and clinical assessment.