This quantitative study examined the achievement gap in mathematics through the analysis of standardized test scores from a suburban school district in Saint Louis County. The problem this study addressed is that students of color in Missouri continue to score well below their peers on mathematics assessments (Bohrnstedt et al., 2015; Kotok, 2017; Paschall et al., 2018). This limits their ability to work toward a high school diploma and causes them to be less competitive in professional fields than their peers (Libassi, 2018; U.S. Census Bureau, 2019). The purpose of this study was to analyze the Northwest Evaluation Assessment (NWEA) MAP Growth composite Rasch Unit (RIT) scores, including RIT scores over the course of five years from a suburban school district in St. Louis County between students' first grade and eighth grade years to identify grade levels in which a significant gap in scores occurs between students of different races. Likewise, this study identified significant changes in RIT scores for each race individually between grade levels. This study identifies trends that school district leadership can use to reconsider their understanding of the achievement gap and work to better meet the needs of all students in similar suburban districts. The standardized test scores were analyzed using an ANOVA test, comparing each race to their peers that were not within their racial group. The scores were then disaggregated by racial group and grade level and analyzed using paired samples t tests to look for significant growth between consecutive grade levels. The ANOVA tests showed significant gaps between scores of African American and non-African American students, Asian and non-Asian students, and White and non-White students, for each grade level included in the tests. The paired samples t tests showed significant growth between each pair of consecutive grade levels for each racial group included in the study. [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.]