The shift from teacher-centered to student-centered instruction requires language teachers' role to change from being lecturers and controllers to facilitators and advisors. This shift requires students to have a high degree of learner autonomy. However, some teachers hesitate to promote learner autonomy. If they remain uncertain about the significance of learner autonomy and its impact on student achievement, they will likely avoid promoting learner autonomy. This quantitative non-experimental correlational study investigated the relationship between students' level of learner autonomy and their achievement on Arabic listening and reading In-Course Proficiency Tests (ICPTs). This research investigated the topic of learner autonomy through the lens of andragogy, an adult learning theory. The participants were 86 U.S. military service members learning Arabic and its dialects as a foreign language in the Arabic Basic Course at the Defense Language Institute Foreign Language Center in California, USA. A learner autonomy Questionnaire (LAQ) was used to determine the students' level of learner autonomy. The collected LAQ and ICPT data were analyzed by SPSS Version 25. Bivariate Pearson correlation and linear regression tests determined the relationship and its predictive power between the LAQ and ICPT variables. The findings confirmed that high scores on the LAQ were positively and directly associated with high scores on the listening (r = .234, p = .03) and reading (r = .259, p = .016) ICPTs. However, the predictive power of the LAQ to predict students' results on the listening ([beta] = .23, p < .05) and reading ([beta] = .26, p < .05) ICPTs was weak. The study concluded that promoting learner autonomy in learning Arabic and its dialects is essential due to its impacts on students' scores on the proficiency tests. The recommendations aimed to enhance teachers' and learners' awareness of the importance of learner autonomy and encourage teachers to promote learner autonomy in their instruction. [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.]