Through instructional tasks, teachers can present content in ways that require students to apply critical thinking, problem-solving, and other cognitive skills. The purpose of this mixed methods collective case study was to determine how teacher-assigned instructional tasks in mathematics impact students' learning of mathematical concepts. In this study, the mathematical tasks assigned by three teachers were evaluated and classified according to the Task Analysis Guide. In addition, the researcher proposed a framework that will assist teachers in assessing the appropriateness of instructional tasks to ensure student learning of concepts. A cross-comparison of each case teacher's data was conducted to provide a comprehensive account of the teacher's task selection and its impact on student learning. The study revealed that teachers are assigning more procedural tasks than conceptual. Student achievement in mathematics can be positively impacted by building procedural fluency, providing more exposure to tasks, and ensuring task appropriateness. The results of this study will improve the instructional practice of teachers and the tasks that they engage students in. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]