Youth portfolios are curated collections of projects that highlight learning across settings over time. Key challenges for harnessing portfolios in broader assessment efforts include the need to better understand what motivates youth to create portfolios and how to leverage these motivations widely. Building on sociocultural approaches, this article presents a qualitative study of youth motivations for portfolios across three US-based school and out-of-school makerspaces. The research identified three themes of youth motivations and how to support them in widespread portfolio assessments: (1) recognition, participating in and contributing to communities outside the makerspace; (2) emulation, modelling professional work practices; and (3) exploration, examining the broader media production pipeline. This work unsettles assumptions of traditional assessment by highlighting the role of capturing episodic engagement to represent youth’s roles in society.