Strengthening political knowledge and democratic understanding of children is an essential aim of citizenship education. In Germany, most curricula of civic education target high school students, neglecting younger children in elementary school. The present study investigates the impact of an out-of-school program for elementary school students at a state parliament on their political knowledge and political interest. The program introduces the students to parliamentary institutions, processes, and decision-making. Among other didactical elements, the students participate in a simulation of a plenary session. The article examines the short-term and long-term effects of program attendance with a quasi-experimental design. The findings show that the out-of-school program positively affects children's political knowledge and interest, thereby confirming that civic education can already be effective at the elementary school level. By implementing such interactive learning programs, schools and teachers could positively contribute to young citizens' political socialization.