Curriculum development is an ever-changing process for educators. As the state and national standards change, curriculum has to be modified to meet the standards. The problem this study addressed the lack of student growth in mathematics through the use of textbook written curriculum compared to the student growth in mathematics through the use of teacher-created curriculum units of study. The researcher specifically investigated the area of mathematics in one elementary school building in a rural Missouri school district. Curriculum was being implemented in different ways throughout the first through third grades in this particular building. The purpose of this quantitative study was to examine whether students were showing similar growth in mathematics through the use of teacher-created curriculum units of study in the curriculum, through the use of textbook written curriculum, or through both. By conducting this research, the researcher will be able to provide the school being studied with valuable information about how curriculum implementation impacts student learning in the building. The researcher used four years' worth of data to complete this study. There were two groups that were tracked throughout first through third-grade. The groups showed a significant difference in student mathematical achievement between teachers using teacher-created curriculum units of study for instruction versus teachers using textbooks for instruction. Additionally, the researcher used three different ANOVA tests to compare the groups' scaled scores. The groups showed a significant difference in student mathematical achievement between teachers using teacher-created curriculum units of study for instruction versus teachers using textbook series for instruction as it relates to scaled score (SS) in Grades 1 through 3. Based on these results, the researcher concludes teacher-created curriculum units of study are better for student learning 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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]