There are many reasons why children have difficulties with mathematics. Dyscalculia is one of them. Teachers need to know what dyscalculia is in order to effectively assist the child to overcome the challenges it presents. However, the literature on the remediation of dyscalculia is in its infancy. The potential for multidisciplinary research is great, but would require maths educators to become involved in this issue, where previously they have been silent. Successful teachers know their students and value knowledge that will help them to help their students. As well as knowing what dyscalculia is, teachers need to understand its causes and have effective strategies to deal with it. Teachers also need to know how dyscalculia affects a child's self-belief system in order to counter the potentially devastating effects of poor self-esteem. Reportedly, there is an incidence rate of 5% in Australian schools, yet there is a lack of recognition, identification and diagnosis of dyscalculia despite the fact that the behavioural characteristics of dyscalculia are well defined and generally agreed on. There are a number of reasons why the diagnosis of dyscalculia is masked. The existence of another (possibly previously diagnosed specific learning disability) is one of them; for example 50% of dyslexics have dyscalculia. This paper seeks to address the ''who, what, how and why'' of dyscalculia.