The purpose of this study was to determine whether relationships existed between teachers' implementation of two specific discourse-related instructional practices and students' mathematics achievement in geometry and measurement as part of a research study on the effectiveness of an advanced mathematics curriculum for kindergarten and Grades 1 and 2. The mathematics units incorporated the following instructional practices: engaging students in verbal communication in mathematics and encouraging the use of appropriate mathematical vocabulary. Hierarchical linear modeling was used to determine the relationships between teachers' use of the instructional practices and the students' mathematics achievement. Results indicated that significant, positive relationships existed; the teachers' implementation scores for the verbal communication and encouraging mathematical language instructional practices were predictors of student mathematics achievement as measured by students' percentage gain scores on the Open-Response Assessments. Implications of these findings for mathematics instruction are discussed.