Abstract: Accuracy is essential in the diagnosis of mathematical difficulties faced by student if we are to intervene and provide appropriate remediation. Yet often times, diagnosis of students’ mathematical difficulties are assessed merely through their written work or monthly assessments only. This article discusses the inadequacies of merely assessing students’ written exercises and highlights the student concerned. Some essential interview strategies such as illustrations, redirection, generalization and questions are include to assist teachers gain insights into their students’ mathematical understanding. Suggestions in administering an interview for various mathematical concepts are also included.