The information society has raised the value of numeracy. This is a challenge to schools and societies, because individual differences are large already in basic number sense and calculation skills. Approximately 5-7 % of school children have extensive difficulties to keep with the speed of curricular demands, i.e. one child in every classroom. These children often have difficulties in other areas of learning too, but disorders in learning can also manifest only in mathematics. Undiagnosed and untreated mathematical disorders become a lifelong handicap creating a barrier to vocational education. They also hinder independent management of mathematical activities of daily living. Low numeracy is a measurable social problem. Intensive and early special education or neuropsychological rehabilitation can diminish the negative effects of the disorders.