The learning climate in the classroom has a very important role in encouraging optimal learning processes in the classroom. The purpose of this research is to look at creating measurements of classroom climate, investigate the aspects that influence it and the role of classroom climate in citizenship education lessons in terms of students' knowledge, attitudes, and behaviour. This study was a factorial design analysis investigating the role of citizenship education classes in classroom climate, students' knowledge, skills, and dispositions. The sample was conducted on 650 junior high school students with a total of 50 classes. Data analysis used was variability correlation and hierarchical linear model analysis. Findings show that a classroom climate with open discussions has proven effective in improving student learning outcomes in citizenship education subjects, both in the aspects of students' knowledge, attitudes and behaviour. Several aspects that influence the level of reliability of measuring classroom climate are the gender composition in the class, the level of student activity, individual perceptions of learning opportunities, the socioeconomic level of students, the level of student knowledge about citizenship education, and differences in views about class material. Thus, an open classroom climate is able to increase student competence in the field of citizenship education and the reliability of the classroom climate is influenced by various factors, including student characteristics at both the individual and class levels. This research has several limitations, including the survey only focusing on students, not involving variability factors from outside the classroom, and not optimally controlling aspects of student response variability. The findings implied that teachers and stakeholders must pay attention to factors that influence the reliability of classroom climate in order to optimally improve academic competence.