Mathematical communication competence was mentioned the first time in the Mathematics curriculum of Vietnam, which was published in 2018. It includes different skills such as listening, reading, presenting, expressing mathematical ideas, and knowing how to use mathematical language to communicate, discuss interaction with other people. The problem is how to organize teaching to promote mathematical communication. In 2004, Radford and Demers based on the theory of Zones of Proximal Development [12] to develop a teaching strategy called the fourth strategy [9]. This teaching strategy has seven steps; it provides groups of the student with different activities to discuss, exchange, review their learning products. We have adopted this teaching strategy in a teaching situation about the concept of function in junior high school in Vietnam. Twelve students who participated in our study case worked in pairs. This teaching process focused on each group of two students reviewing products of another and basing on comments from other groups to improve their products. Furthermore, our teaching situation puts students in front of the various representations of function and thus enhances the use of mathematical language and mathematical communication for students. The results of our study showed that the teaching strategy of Radford and Demers increased students' mathematical communication. Lessons drawn from the study are that this strategy is really an effective teaching method if teachers assign open problems that stimulate the curiosities of students; in the classroom, they feel free and confident in discussion; if these conditions are met, students who learn in this approach will acquire and reinforce the knowledge as a result of a mathematical communication process.