Prototyping in design provides ways to navigate ambiguity in the design problem, gain insight through the refinement of ideas, and aid in communication between team members. However, while designing, students often underutilize prototyping and do not consider it as an integral part of the design process. To facilitate the scaffolding of design activities, it is necessary first to understand students' conceptions of prototyping. In this study, we use artifact elicitation interviews as a method to elicit students' conceptions by moving from the specifics of the artifacts they brought with them to the interview, to their general understanding of prototyping. Participants in the study are students in an undergraduate sophomore design-oriented, project-based learning course in a large southwestern university. Students were invited to participate in a screening survey. After potential participants suitable for the purpose of this study were identified, some were selected for a follow-up interview. The findings of the study describe students' conceptions of 'what counts' as a prototype; what is valued in a prototype; the benefits of, and challenges associated with prototyping; and differences between in-class and out-of-class prototyping activities. The findings of this study improve our understanding to effectively scaffold prototyping activities in design and experiential learning.