The present study explores the ways in which young people’s relationships with adults and peers as well as their ability to express agency within their school environments influence their academic mindsets. Using a nationally representative sample of 3,300 high school aged youth, this study first investigates the ways in which the independent mindsets associated with an academic mindset (i.e., a sense of belonging, a growth mindset, self-efficacy beliefs, and the belief that one’s work is meaningful) are related to one another, and then explores the ways in which positive school based relationships and expressions of agency within their school environments contribute to those belief systems. The study is grounded in relational developmental systems theory and employs a positive youth development framework to understand the ways in which interpretive and recursive person-context developmental relations contribute to young people’s beliefs about themselves, their educational environments, and themselves in relation to those environments. As educational practices increasingly shift towards deeper learning and a whole child educational paradigm, understanding the ways in which relationships and expressions of agency influence positive academic mindsets may aid in enhancing educational experiences for all young people. This study finds that all four beliefs under consideration load onto the higher order construct of academic mindset, that relationships with both school adults and peers are positive associated with academic mindset, and that agency fully accounts for the association between relationships with adults and academic mindset, and partially accounts for the association between relationships with peers and academic mindset. Implications for policy and practice are discussed.