This study explores students' mathematical reasoning within a novel technological environment designed to support understanding of relationships between quantities and adjustable measuring units. In particular, 30 elementary students (grade 3-5) engaged in a series of measurement tasks in which they used a "dynamic virtual ruler" that could be continuously dilated. Students' reasoning patterns were characterized using four distinct levels, and analysis also attended to their various uses of the dynamic technology. Additionally, I articulated possible mechanisms for shifts in strategies across the tasks from both instrumental and semiotic approaches. My findings will contribute to education fields by providing a theory-driven, empirically-tested set of tasks that can be used to introduce fractions is an alternative way in elementary mathematics classrooms, and eventually drawing insight for students to use dynamic technology meaningfully. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]