Abstract
Mathematical justification, the act of giving arguments to defend a claim, strongly supports students’ Collaborative Problem Solving (CPS). Yet studies exploring justifications in a heterogeneous-achievement group are still limited. This study describes mathematical justifications of such a group in CPS by identifying the levels of justification and the role of each student. The findings showed that the group used perceptual demonstration to generalisable arguments level of justifications. Higher-achievement students were found initiating justifications, while lower-achievement students triggered or merely accepted them.