Classification of arithmetic disorders is predicated on neuropsychological features and associated learning disabilities. Assesses the compatibility of these classifications on a nonreferred, population-based cohort of children (N=139) with developmental dyscalculia. Concludes that children with dyscalculia and disabilities in reading and/or writing are more profoundly impaired in arithmetic than children with dyscalculia alone or attention deficit hyperactivity disorder. Contains 36 references. (Author/ASK)