Yet many agency stakeholders lack awareness of strategic best practices to ensure the consistent and meaningful participation of young people in decision-making processes, and few tools exist to evaluate agency efforts. This paper describes the development and validation of the Youth/Young Adult Voice at the Agency Level (Y-VAL), an assessment of the extent to which agencies have implemented best practices for supporting meaningful participation. The Y-VAL is intended for research purposes, as well as to provide agencies with direct guidance about strengths and challenges regarding their efforts to promote youth/young adult voice.