In an attempt to examine dialogue within a second grade classroom, students were encouraged to participate in whole-class mathematics discussions without raising their hands before speaking. Beneficial social and sociomathematical norms developed in place of this traditional social norm. Effects of this change on the dialogue and written mathematical explanations of a class of second grade students are described. Focus was placed on student participation in whole-class discussions. The study helped to determine the effects of student-centered dialogue on students' mathematical explanations and justifications as demonstrated in the students' discussions, participation, and written expression related to their mathematics learning. (Contains 4 figures.)