This study concentrated on the characteristics of Grade 2 students' writing in mathematics class who used the Project M[superscript 2] units to learn geometry and measurement. Included in the study were students with high and low levels of content knowledge. Archived data from the Project M[superscript 2] study were analyzed to determine the extent to which the use of the Project M[superscript 2] units impacted the mathematical writing of Grade 2 students with respect to how they formulated written arguments on an end-of-the-year assessment. Using a MANOVA, archived data of students' writing that represented the students who experienced the Project M[superscript 2] units were compared to a comparison group of students who did not experience the Project M[superscript 2] units. The results of the end-of-the-year assessment indicated that the Grade 2 students who used the Project M[superscript 2] units outperformed a comparison group in their ability to (a) reason and justify their mathematical thoughts, (b) attempt to use mathematical vocabulary, and (c) correctly use mathematical vocabulary. Their written responses indicated no difference with the comparison group in their ability to use specific elements of language arts in their writing (complete sentences, attempt at writing). Based upon this study, the findings indicate that the use of the Project M[superscript 2] units at the Grade 2 level had a positive effect on students' ability to write in mathematics. Though future studies are needed to identify the components that may have had more of an influence on student writing, the results suggested that the components as a whole positively impacted student writing in mathematics. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]