Public participation in local decision-making processes has numerous purported benefits. Yet, realizing these benefits requires a citizenry that is able and willing to participate in meaningful ways. High schools are ideal venues for civic education but rarely teach local collective action, citizen engagement, and self-governance, focusing instead on personal responsibility, knowledge of political institutions, and information on the electoral processes. This article reports on a citizenship education project in a high school in Phoenix, Arizona. The program engaged students from all grade levels in a participatory budgeting (PB) process--to our knowledge, the first School PB in the U.S. The study asked to what extent student engagement in PB contributed to democratic learning necessary to actively engage in public debates and decision-making processes. The findings suggest that deliberative processes that engage students in decision-making can develop civic competencies, and among available strategies, PB is particularly effective. The study also found that the impact of informal democratic learning through PB increases significantly when it is paired with formal learning in the classroom.