Educators are often looking for ways to increase engagement and academic achievement in their classrooms; therefore, the problem addressed in this study is the decrease in academic achievement caused by a low level of classroom engagement amongst high school seniors. The purpose of this qualitative action research study is to increase academic achievement in the classroom through student engagement using adult learning principles. In 1970, Malcolm Knowles brought attention to the idea of andragogy, thus promoting five principles of adult learning: self-directed learning, relevancy of material, problem-centered learning, motivation to learn, and application of real-life experiences. Applying these adult learning principles in a twelfth-grade classroom may possibly increase student engagement, thus increasing academic achievement. Four participants from rural schools in the Midwest United States participated in this action research. The research took place over the course of four weeks, and data were collected through structured interviews. After a thorough analysis of the data using a coding process, five themes emerged: (a) academic achievement is defined differently among teachers; (b) formative and summative assessments measure academic achievement; (c) there is a connection to engagement and academic achievement; (d) engagement is seen in similar ways across subjects; (e) academic achievement and engagement in the classroom are increased with the use of andragogy. An overall consensus showed an increase in engagement and academic achievement when Knowles' adult learning principles were used in a twelfth-grade classroom. Using this research and results, training and workshops would be beneficial for educators to understand and implement adult learning principles in the classroom to increase engagement and academic achievement for both veteran and novice teachers. All four criteria of trustworthiness were met in this study. [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.]