This large-scale study investigates the effectiveness of a Comprehension-Based Language Teaching (CBLT) program implemented across educational institutions affiliated with the Turkish Armed Forces. Using a quasi-experimental pretest-posttest design, data were collected from 8,522 students via the Oxford Placement Test (OPT) to evaluate language proficiency gains over one academic year. Results indicate statistically significant improvements in students' scores, with an average gain of 10.4 points (Cohen’s d = 0.87), particularly marked among beginner-level learners. Ninth-grade students demonstrated the highest gains, ranging from 11.6 to 16.7 points. When compared with students from national and private schools receiving traditional integrated skills instruction, military students outperformed their peers by a factor of 7.4 despite receiving 77% fewer instructional hours. A key moderating factor was teacher training: institutions with well-trained CBLT instructors showed 23% greater student gains than those with minimally trained staff. These findings strongly support input-based language acquisition theories and point to the critical role of instructional quality. The study concludes with recommendations for language education reform in Turkey and similar EFL contexts, emphasizing the strategic adoption of comprehension-based methodologies and robust teacher training frameworks to enhance learner outcomes across educational settings.