Mathematical learning and teaching are increasingly seen as a multimodal experience involved in cultural and social semiotic registers and means, and as such social-cultural semiotic analysis is expected to shed light on learning and teaching processes occurring in the mathematics classroom. In this research, three social-cultural semiotic frameworks were utilised to analyse elementary school students' learning of a geometric relation: the semiotic bundle, the space of action, production and communication and the theoretical framework of attention, awareness and objectification. Educational mathematical situations are described, in addition to semiotic sets, registers and means emerging in the different mathematical situations and that are relevant to the three social-cultural semiotic frameworks which the current research utilizes. Further, the students, as a consequence of (1) their multimodal experience, (2) their connecting between the different mathematical situations and semiotic registers, and (3) the teacher's questions and tasks, could objectify the geometric relation between the lengths of the triangle's edges.