Is a specific disorder of arithmetic skills as common as reading/spelling disorder?

Referring to the prevalence rates of learning disorders in the research literature, the numbers of mathematics disorder and reading/spelling disorder are often reported to be identical. However, the correlation between intelligence level and reading/spelling skills is much weaker than between intelligence and arithmetic skills. If the same definition criterion is applied to both disorders, a lower prevalence rate for mathematics disorder should be expected. Are there differences in the prevalence estimates for learning disorders depending on the definition criterion? A large representative sample of German students (N=1970) was used to review the hypothesis. Depending on the definition criterion, we could show a prevalence range of mathematics disorder between 0.1% and 8.1% in the same sample. Using the same definition criterion for both learning disorders, there are two to three times as many students with reading/spelling disorder than those with mathematics disorder. Whenever children with reading/spelling disorder are compared to children with mathematics disorder, the same definition criterion has to be applied.