The purpose of this study is to explore a conceptual approach to assessment for one-shot library instruction. This study develops a new assessment instrument based on Carol Kuhlthau’s information search process (ISP) model. The new instrument focuses on measuring and identifying changes in student readiness to do research along three dimensions—cognitive thoughts, affective feelings, and research actions—before and after the students receive one-shot library instruction at the beginning of their research. The development of the new instrument includes a validation process supported by statistical analyses. The results demonstrate that the students improved their research readiness after receiving one-shot library instruction.