Developmental dyscalculia: Precursors, prevalence, and co morbidity

The current study investigated the prevalence of developmental dyscalculia (DD) in a representative population based sample (N = 337) of children in grade 2 from the Kanton of Zurich (CH) within a longitudinal design. Assessment of numerical abilities used revised versions of the Neuropsychological Test Battery for Number Processing and Calculation (ZAREKI) in kindergarten (-K) and second grade (-R). First testing took place in the last year before entering school (mean age: 6;5 years). Retesting was done two years later (8;7 years) and included assessment of reading and spelling abilities. A prevalence rate of 1.8% for pure developmental dyscalculia (pDD) and 4.2% for combined mathematics and reading/spelling disorders (cDD) was found, resulting in a total prevalence rate of 6% for DD. pDD was obviously less frequent than pure reading/spelling disorders (prevalence: 5.7%). Affected children already showed a weaknesses in numerical precursor abilities at kindergarten age. Comparing the test profiles at the two different testing times indicated that children of the cDD group showed an additional weakness, mainly in tasks with high working memory load, compared to the pDD group. At 2nd grade level, teachers perceived children with DD to be significantly more inattentive and hyperactive compared to normally achieving children. Results will be discussed regarding current developmental models of number processing and calculation.