Although experiential approaches to democracy education are gaining increased support from educators and scholars, few educational resources exist to support youth in constructing and delivering high-quality, evidence-based policy arguments to authentic audiences. Such presentations are often the first time that young people step into the public sphere and speak to public officials; they represent rich opportunities for youth political development and activism. In this paper, we introduce an assessment tool, called the Measure of Youth Policy Arguments (MYPA), which is intended to be a resource for community and school educators. Drawing on data from two years of field-testing and iterative co-design in the context of research-practice partnerships (RPPs), we chronicle the development of the tool and provide evidence about its educational uses in classrooms and community programs. In the discussion section, we explain key decisions in the development of MYPA and how those shaped its appropriateness for certain uses and lack of appropriateness for others.