Ability grouping in education is a common practice used to differentiate instruction in order to meet the academic needs of students. The primary purpose for grouping students by ability is to increase their academic growth and achievement by providing instruction at the students' current instructional level. However, there is much conflicting research regarding the impact of grouping students by ability and its link to student achievement. The purpose of this study was to determine if there is a statistically significant difference between school-wide student achievement in grades 3, 4, and 5 based on the type of grouping: ability grouped or not grouped by ability classroom settings. Data were collected from the Tennessee Department of Education website for the 2012-2013 academic school year as well as from individual school administrators regarding how students were grouped for instruction: grouped by ability or not grouped by ability. Independent samples t-tests were run to determine if there is a significant difference between students who received instruction in ability grouped setting and those that were not placed in an ability grouped classroom. The results of this study indicated that there is no difference in achievement scores based on the type of instructional setting (ability grouped or not grouped by ability) in reading and math in grades 3, 4, and 5. [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.]