This study analyzes the relationship between youths’ conceptions of citizenship and their conceptions of mathematics in order to understand the role that mathematics can play in the development of youth as citizens. The study also explored the possibilities and challenges of a social justice mathematics approach in the development of youth as citizens. Individual interviews were conducted with a total of 38 students from two research settings: a middle-school mathematics class in a public school in a low-income neighborhood serving primarily Black youth, and a mathematics class at an alternative educational program for out-of-school youth obtaining their GED serving primarily a low-income Latino population. An analysis of students’ conceptions of citizenship using Westheimer and Kahne (2004)’s framework highlighted the prevalence of personally responsible conceptions of citizenship across both settings. Having students discuss issues in their communities prompted students to also suggest participatory actions, and engaging in discussions about issues of injustice specifically yielded justice-oriented responses. Personally responsible responses and even participatory responses were often coupled with a sense of powerlessness, as they focused on addressing symptoms of issues by changing or controlling individuals’ behaviors. Students’ conceptions of mathematics also reflected personally responsible conceptions of citizenship. Examining students’ conceptions of mathematics revealed that students have a limited perspective of the role of mathematics in the world, such as in applications involving money, daily tasks, and careers. Students from both settings, but especially those from the alternative education program, also expressed that the mathematics they learn in school primarily serves a credentialing role. Mathematics for social justice offers a promising means to empower youth as justice-oriented citizens by showing them how mathematics can play a key role in learning about and making change in the world. In their reflections about mathematics for social justice lessons, students expressed that mathematics validated their experiences and provided powerful evidence to use in pressing authorities to listen to their issues.