This action research study describes the impact of ability grouping on fifth-grade students' academic achievement in reading. The theoretical framework that supported this study is embedded in cooperative learning, social learning, social interdependence, and self-efficacy. This study used a mixed methods design to consider the following research questions: "How does ability grouping and the use of i-Ready learning system impact students' academic achievement in reading in a fifth-grade classroom?" The study also examined the impact that reading had on students' confidence through a second research question: "What is the impact of ability grouping as it relates to students' reading confidence?" A third research question was examined to understand the impact of reading had on students' confidence: "What is the impact of ability grouping as it relates to students' attitudes toward working in reading groups?" The participants of this study included a class of 27 students. Data was collected through pre-and post-questionnaires, student focus interviews, and i-Ready diagnostic scores. [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.]