Over the history of interaction design, concepts and methods of prototyping have been significantly developed to address new challenges faced by the field and the ever-going advancement of new technologies. Some of the important developments are related to the notions of mixed-fidelity prototyping, experience prototyping, and prototypes as filters. Building upon these developments, this study explores a multiple-fidelity prototyping approach, that is, using progressively higher fidelity prototypes in iteration. The study focused particularly on the design of user engagement. It documented, and contributed to, an actual design process of Xplore, an augmented reality game-based learning application. Three participatory design-style workshops employing low-, mixed-, and high-fidelity prototypes were conducted respectively. Thematic analyses of participants’ interactions revealed sets of themes in the workshops, which reflected the changing focus and scope of the design space. The implications of the results obtained in the study highlighted the role of prototypes of each fidelity level in engaging users in a design process, as well as the potential benefits of combining multiple fidelity prototypes when designing for user engagement.