Many students experiences difficulties in learning and applying mathematics and require assistance to overcome the misconceptions or inappropriate ways of thinking they have developed. Underlying causes of any difficulties need to be determined, students need to be led to see inadequacies in their ways of proceeding and thus appreciate a need to change, so that appropriate ways of thinking, generalising and applying mathematical ideas can be developed and implemented through well-focused processes of diagnosis and intervention. In this way, students can be helped to develop the conceptual understanding and fluent processes needed to acquire and use mathematics so as to become numerate.