Background/Context: Over the last two decades, youth involvement in policy advocacy has increased sharply, through youth councils, organizing coalitions, and new media forums. Currently 12 states and 140 American cities have youth councils or commissions established to advise policymakers on the impact of their legislation on youth. Despite their growing presence, we know little about what these councils do, how they are viewed, or how, if at all, they influence policy-making processes. Purpose: This study explores manifestations of adultism during the first 4 years of the Ballou City Youth Commission (BCYC) from the perspectives of 22 youth members and adult allies. Research Design: Though primarily interview-based, this study also draws on field notes collected during a BCYC meeting and a BCYC community forum and organizational artifacts to explore the nature and dynamics of adultism as they played out in BCYC. Data Collection and Analysis: In-depth, individual interviews were conducted with 11 current and former youth commissioners and 11 adults who represented the target audience for BCYC's work or who partnered with the commission on various initiatives. The theoretical framework of adultism guided the analysis, which included open and axial coding, memo writing, and the construction of matrices and charts to track emergent patterns. Findings/Results: Using a critical theory lens, we find that adultism has played a prominent role in limiting BCYC from achieving the goals laid out in its charter. We identify a "roller coaster of adultism" that illustrates how weak initial structures coupled with deeply entrenched views of youths' limited capacity adversely impacted the functioning of BCYC and propelled a cycle of externalized and internalized adultism. Conclusions: The study adds to the scant literature on youth voice in public policy, raises six clear implications for policy and practice, and extends theory by illustrating the complex ways in which external and internalized forms of adultism interact with and reinforce each other.