This study investigated Spanish-speaking kindergarten students' participation in mathematical discourse as they solved and discussed a range of word problems. Specifically, we draw upon sociocultural perspectives on mathematics learning to frame mathematical discourse and to examine specific teacher and student actions that seemed to support the development of mathematical discourse over the course of the kindergarten year. Data sources included pre- and post-task-based clinical interview assessments and weekly (videotaped) observations of problem-solving lessons. Findings demonstrated ways that teachers supported and students appropriated discursive habits such as using more precise mathematical language, explaining solutions in ways that referenced actions on quantities in the problem, and using multiple visual representations to mediate communication. In addition, the findings point to the critical role the teacher plays in supporting the development of students' mathematical discourse. (Contains 8 footnotes.)