This study aims to investigate students’ mathematical communication skills through investigating their defining, using mathematical concepts and mathematical language skills. Additionally, this study aims to investigate the relationship between students’ mathematical communication skills with their academic achievements. A seventh grade classroom at a public middle school in the province of Erzurum and 34 students and their mathematics teacher participated in the study. Students were asked to keep journals during seven weeks for sixteen Geometry standards after each standard. Student journals were analyzed in four hierarchical levels—Level 0 (Avaoidance), Level 1 (Incorrect Use), Level 2 (Incomplete Use) and Level 3(Correct and Complete Use) — by two researchers individually. Later, the researchers compared their categorizations and discussed till solving the disagreements. According to the findings of the study, participating students did not comprehend the concept definitions. It was seen that students attempted to use mathematical language in their journals as a way of communication. However, it should be noted that some incorrect use of mathematical language was apparent in student journals. This study also showed that it was hard to conclude that student mathematical communication skills differ based on their academic achievement levels.