Civic knowledge is critical to interpreting various policy and candidate issues that are necessary to participating in certain political activities, such as voting in elections or attending public demonstrations. Various studies have examined students' perceptions of classroom openness, which reflects perceived levels of political discussion supported by peers in the classrooms, to understand how this measure relates to students' civic behaviors. This study analyzes data from the 2009 International Civic and Citizenship Education Study, in which approximately 134,000 students were sampled from 38 countries across Europe, Asia, and Latin America. Results from three-level hierarchal linear modeling suggest that students' perceptions of classroom openness are strongly related to their civic knowledge scores. Further analyses indicate that the relationship strength between these two measures do not vary across students from different socioeconomic backgrounds. These findings reaffirm the importance of curricular approaches that emphasize political discussions in classrooms to prepare students for active citizenship.