Developmental dyscalculia: prevalence and demographic features.

One hundred and forty-three 11-year-old children with development dyscalculia, from a cohort of 3029 students, were studied to determine demographic features and prevalence of this primary cognitive disorder. They were evaluated for gender, IQ, linguistic and perceptual skills, symptoms of attention-deficit hyperactivity disorder (ADHD), socio-economic status and associated learned disabilities. The IQs of the 140 children (75 girls and 65 boys) retained in the study group (three were excluded because of low IQs) ranged from 80 to 129 (mean 98.2, SD 9.9). 26 per cent of the children had symptoms of ADHD, and 17 per cent had dyslexia. Their socio-economic status was significantly lower than that of the rest of the cohort, and 42 per cent had first-degree relatives with learning disabilities. The prevalence of dyscalculia in the original cohort was 6.5 per cent, similar to that of dyslexia and ADHD. However, unlike these other learning disabilities, dyscalculia affected the two sexes in about the same proportions.