This mixed methods action study examines the relationship of students' three psychological needs of autonomy, relatedness and competence as presented in the Self-Determination Theory (Deci & Ryan, 1985) to the level of achievement of high school seniors at Litchfield High School. In the quantitative phase of the study, the quantitative research questions examine the relationship between self-determination as measured by the Basic Needs survey and achievement as measured by the ACT scores of sixty-one Litchfield High School twelfth grade students. In the qualitative phase, three separate focus groups made up of twelve seniors who participated in the Basic Needs survey and who were in one of three groups determined by their ACT scores discuss their insights on motivation. This research provides insight into student perceptions of self-determination and motivation and implications to aide administration, faculty and staff in developing intrinsic motivation in high school students. [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.]