Student achievement in mathematics, particularly in urban areas, is a consistent concern in the United States. Research suggests that teachers either are under qualified or have a negative perception of themselves as mathematics teachers. Departmentalization on the elementary level is an organizational structure that may benefit urban students and teachers in the area of mathematics. The results of the few studies on departmentalization in elementary school mathematics are mixed, The purpose of this study was to use a correlational research design to determine a relationship between type of classroom instruction and student achievement. School level fifth-grade student achievement from 46 schools was compared using the 2011 Georgia Criterion-Referenced Competency Test (CRCT). Moderating school variables were (a) percentage of students eligible for the free and reduced lunch program (FRL), (b) percentage of minorities, and (c) school size. The results indicated that mathematics scores were not predicted by school size or organizational structure. Schools with different percentages of FRL did not perform differently in the two types of classroom settings. Research supporting specialized mathematics teachers or departmentalization at the elementary level indicates that it would be more attainable to improve mathematics knowledge of a few elementary teachers rather than attempting to improve the entire teaching force. In this study, teacher knowledge was not considered; including this variable in future studies may worthwhile, Additional studies on the influence of SES (or FRL) on organizational structure in elementary settings would be beneficial, Teacher quality, preparedness, effectiveness, efficacy, and experience were not considered in this study. FRL provides a partial picture of students who come from disadvantaged backgrounds, but does not fully capture all dimensions of poverty. Including additional variables (i.e., demographics of the school's neighborhood and percentage of single-parent households) may provide a better picture of poverty. Although this study did not find differences between organizational structures, the practice of departmentalization is still worth investigating. Due to the continued increased demands in teacher accountability and higher standards for mathematics instruction, specialization or departmentalization may be a required trade-off to the relationship building often referenced in self-contained settings. [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.]