In other words, developmental dyscalculia is a disorder of mathematical ability, seen in children of normal intelligence. Further, the disorder, according to Kosc, has a biological basis and possibly a genetic aetiology, in which case there should be positive family histories of developmental dyscalculia. From a cognitive neuropsychological viewpoint, a further element of Kosc's definition is of interest, since he proposes a direct biological relationship between the parts of the brain implicated in developmental dyscalculia and the par ts of the brain employed for mature mathematical abilities. Within cognitive neuropsychology, a functional analogue of this view would propose tha t with developmental dyscalculia there is developmental impairment in modules of the calculation system, which had they matured would have formed modules of the adult calculation system. Such a view implies
hard-wiring of the biological substrates of calculation modules. This chapter will explore the developmental dyscalculias and discuss the behavioural data relevant to this debate. The following key questions are of relevance. Is it possible to explain the developmental dyscalculias in relation to a cognitive model of normal function? Is there evidence of independence or semi-independence in the establishment of components of the calculation system? Are there limitations to functional plasticity in relation to the developmental dyscalculias? Is there a single route to competence or alternative pathways?