This article examines the process by which Japanese came to be solidified as the national language of instruction in public schools during the first decade of colonial rule (1911–22). First, I analyze Government-General of Korea language policy and the recollections in 1917 by the policy insider Oda Shogō, which reveal a confidence in the efficiency of administration but also a tension between the official discourse on Japanese language nationalization and the perceived proficiency of Korean instructors and students. The March First Movement less than two years later exploded the misconception of a complacent student body and brought to the fore simmering grievances, notably the language of instruction issue in public schools. Through an analysis of the language of instruction debate in the popular press, I demonstrate the rupture that had developed between Japanese officials and the Korean public, an unbridgeable divide due to the impasse between co-educationalists calling for integrated education in Japanese only and “language nationalists” demanding more instruction in Korean. The Second Rescript on Education proclaimed by the Government-General in 1922 thus affirmed the dominant position of Japanese in the curriculum and ensured the continuing vitality of private sŏdang well into the 1920s.