This page describes the technique of using interviews to assess student understanding. The assessment tool is one of a series of Classroom Assessment Techniques (CATs) provided by the Field-tested Learning Assessment Guide (FLAG) website. The CATs of FLAG were constructed as a resource for science, technology, engineering and mathematics (STEM) instructors to emphasize deeper levels of learning and to give instructors valuable feedback during a course. Interviews enable instructors to judge the extent of understanding students have developed with respect to a series of well-focused, conceptually-related scientific ideas. This site provides an overview of this assessment instrument including information about how to use classroom interviews to their maximum benefit. The site is also linked to a set of discipline-specific "tools" that can be downloaded for immediate use, as well as supplementary links and sources to further explore this assessment tool.