This study employs Sfard's (2008) socio-cultural theory of Commognition to analyse student teachers' thinking and communicating practices. Specifically, we investigate the effectiveness of the student teachers' communication of a particular mathematical proof with reference of the four features of the commognitive framework (i.e., word use, visual mediators, narrative and routines). In this paper, we can report on the routine of the discourse to analyse the quality of mathematical discourse in two situations of "Expert-to-Novice" and "Novice-to-Novice".