The purpose of my study was to understand the role of discussion in students' learning of mathematics. I conducted the study at a private school. The teachers reinforce mathematical concepts, which students follow by practicing and drilling. The study was conducted through action research, where I taught lessons by using whole class and small group discussions. I collected the data by audio recording the whole class and small group discussions. I analyzed the data by using the qualitative methods, such as coding the data on the bases of emerging patterns. I found that discussions in small groups provided an opportunity for the students to explain and communicate their ideas to other members and listen to their ideas. In the process of such explanations and communications, the students got an opportunity to formulate and clarify their thoughts. Discussion helped the students to develop their mathematical language skills through participating in group and whole class discussions. I also found that the teacher played a significant role in stimulating discussion in the classroom. For example, I promoted discussion through questions and probing. During the whole class discussions, the teacher's modeling helped the students to learn and use mathematical terms and symbols. Discussion helped the teacher to assess the students' learning through interactive discussions and respond appropriately on the spot.