Children with dyscalculia lack the notion of numbers, of quantities and estimates. They fail especially because of the basic arithmetic operations. Depending on the arithmetic operation involved, the values for children with very great difficulties in this area vary between three and six percent. This is proven by LMU (Ludwig-Maximilian-University) scientists working with Professor Gerd Schulte-Körne in a current study. For the investigation, they made appropriate tests with 1633 school children who were in third and fourth grades in and around Munich.