This paper investigates the impact of social interactions on mathematical language development in children during cooperative learning in a fourth grade mathematics classroom in Ireland. An experimental group completed mathematics activities in cooperative groups, while the control group completed these tasks individually. Participants from both the experimental and control groups were interviewed pre and post intervention. Following intervention, both groups used more specific language and employed a greater quantity and variety of mathematical language. The experimental group had greater ability to express evaluations of their own mathematical practice following intervention. Peer interactions in cooperative groups can assist a learner's development of specific mathematical language.