The shift from teacher-centered to student-centered instruction requires language teachers' roles 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 in Arabic listening and reading as measured by In-Course Proficiency Tests (ICPTs). 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 Monterey, California. A learner autonomy Questionnaire (LAQ) was used to determine the students' level of learner autonomy. Bivariate Pearson correlation and linear regression tests determined the relationship and its predictive power between the LAQ and ICPT variables. The findings indicate that high scores on the LAQ were positively and directly associated with high scores on the listening and reading portions of the ICPT. The study concluded that promoting learner autonomy in learning Arabic and its dialects is essential due to its impact on students' scores on proficiency tests. Recommendations are included and aim to enhance teachers' and learners' awareness of the importance of learner autonomy and encourage teachers to promote learner autonomy in their instruction.