Research from both domestic and international assessments has revealed the problematic nature of mathematics instruction and assessment practice. The method of standardized testing is extremely influential in school psychology, dominating the evaluation and study of children’s thinking. Although increasing numbers of practitioners are relying on curriculum-based measurement (CBM) as an alternative assessment to standardized testing, the procedure used in CBM is notably similar to testing in previous decades in terms of the types of items and the methods of administration. This type of assessment does not allow in-depth examination of children’s dynamic mathematical thinking and development due to its “standardized” assessment procedures. Therefore, the potential for developing effective intervention and instruction to foster children’s mathematics learning is limited. The clinical interview, a powerful set of assessment strategies, presents an alternative, or supplementary method, for the study of children’s thinking and reasoning. Understanding the underlying cognitive processes in children’s problem solving is particularly important in the semantically complex domains in mathematics, such as fractions. Developing the knowledge and skills necessary to conduct clinical interviews are critical in developing evidence-based instruction and intervention in mathematics.