국어
In 1940, Tagalog was approved as the basis of for the National Language of the Philippines. Santos then became the first Tagalog Teacher at NTC. He also taught Tagalog at Baguio Vocation Normal School. He was appointed supervisor of National Language of the Department of Education (Philippines) until 1942, when World War II broke out in the Philippines. During the Japanese Occupation, Santos was offered membership to the Institute of National language which was headed by Lope K. Santos (the two are unrelated). Not wishing to serve the Japanese invaders, Santos rejected the offer. There were attempts by the Japanese police to arrest Santos, but he was always successful to elude them.