In recent years, numerous studies have been conducted on language teachers' beliefs about language assessment; however, teachers' collaborative discussion as a mediational tool has received scant attention. The present study aimed to investigate non-native language teachers' beliefs about classroom language assessment regarding features of effective assessment, assessment of learners by teachers, peers, and themselves, benefits of assessment, informal assessment vs. formal assessment, and continuous assessment. Participants of the study were positioned in two collaborative discussion groups of novice and experienced teachers. Analysis of the data indicated that the teachers in each focus group held similar beliefs about most of the issues on classroom language assessment. The findings also demonstrated that the participants believed in the important role of classroom language assessment for different purposes, the utilization of both informal and formal assessment, and the utilization of continuous assessment as a fair mode of assessment. Furthermore, they believed that classroom language assessment should accurately assess what is taught in the course while focusing on all four language skills and sub-skills. Although they had positive attitudes toward teacher assessment and self-assessment, they were not in favor of peer assessment. The results of this study have implications for teacher education as adequate attention should be paid to teachers' assessment beliefs due to their vital role in classroom assessment. Collaborative discussions can be enacted in teacher education to shape and reshape teachers' assessment beliefs.