While many studies examining the effectiveness of using dynamic geometry software exist, few studies exist at the elementary school level. An extensive data analysis of student performance on New York State Math Assessments revealed that students in the fifth grade may not have had a clear understanding of interior angles sums of polygons, more specifically, quadrilaterals. Could using Geometer's Sketchpad, a dynamic geometry software program, help students perform better on questions about interior angle sums of polygons? For this study, students were divided into four groups using the Solomon Four Group design (Solomon, 1949). Two of the groups experienced lessons using Geometer's Sketchpad (these groups were the experimental groups), while the other two groups received instruction without the use of Geometer's Sketchpad (these groups were the control groups). The investigator observed all lessons performed during the study. Commentary about student interaction during the lessons was recorded and reported. Pre-tests were administered to two of the groups, and all four groups took two final assessments. The first of the final assessments tested interior angle sums of polygons. The second final assessment tested the students' ability to transfer their knowledge to both non-convex quadrilaterals and polygons with more than four sides. Students in the experimental groups significantly outperformed students from the control groups on both final assessments. Students in the experimental groups were better able to transfer their knowledge of interior angle sums to polygons with more than four sides. Additionally, students who had the experience of using Geometer's Sketchpad were able to clear up any prototypical notions about polygons as well as any confusion about comparing relative sizes of angles. Using Geometer's Sketchpad did not seem to help students understand an angle as a turn. [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.]