Teaching mathematics in general and instructing mathematics at junior schools in particular not only create favorable conditions for students to develop essential and core competencies but also help students enhance mathematical competencies as a foundation for a good study of the subject and promote essential skills for society, in which mathematical communication skill is an important one. This study aimed to train students in mathematics communication by presenting them with topics in line with the structure's congruent triangles. An experimental sample of 40 students in grade 8 at a junior school in Vietnam, in which they were engaged in learning with activities oriented to increase mathematical communication. A research design employing a pre-test, an intervention, and a post-test was implemented to evaluate such a teaching methodology's effectiveness. For assessing how well the students had progressed in mathematical language activities, the gathered data were analyzed quantitatively and qualitatively. Empirical results showed that most students experienced a significant improvement in their mathematical communication skills associated with congruent triangles. Additionally, there were some significant implications and recommendations that were drawn from the research results.