Assessment is a topic of concern to all stakeholders in our educational system. Pattern Based Questions are an assessment tool which is an alternative to the standardized assessment tool, and they are based on generative learning pedagogy, which shows promise in engaging all learners and usefulness in teaching and learning but validity has not yet been empirically established. Pattern-based questions seek to provide a qualitative expression of student understanding. It is the purpose of this research to empirically explore a correspondence between student response patterns and the students' expressed ways of thinking using a grounded theory approach and clinical interviews. Findings include rich descriptions of participants' ways of thinking about equivalent fractions as written in the PBQ. One response pattern was clearly differentiated from the others. Future research is discussed. [For the complete proceedings, see ED657822.]