The aim of this study is to design and develop a user-centered, smart-tool prototype that could be used to assist teachers to practice differentiated instruction (DI) in their classrooms. This study also demonstrates how user-centered design process for the development of teacher's tools might be useful to identify system features and to prioritize decisions of the features by making teachers participate in all evaluation processes. For the user-centered design approach, first, conceptually designed personas and scenarios were applied based on user needs and system requirements identified in our previous study. Then, three rounds of iterative evaluations including scenario reviews, claim analysis, and usability testing were conducted by the teachers. Scenario reviews with teachers provided designers with an opportunity to better understand teachers' tasks related to DI, and claim analysis helped to make priorities on the features that designers cannot decide. This study has implications on issues related to student's private information on smart-technology for instruction. Another implication of this study is to demonstrate the merits of different evaluation methodologies, applied and demonstrated here, in order for designers to utilize the methods when designing and developing new tools with future technologies in educational contexts. Finally, through three rounds evaluations, it was validated that the use of smart technologies, such as the developed smart-tool in this study, can promote differentiated instruction in action.