The founding of Triam Udom Suksa School relates to the revised National Education Plan of BE 2479 (1936 CE), which imposed four and six years of
primary and
secondary education respectively, with an additional two years of pre-collegiate schooling required for students who were to pursue higher education. This pre-collegiate level was to be initially provided by the students' prospective universities, and accordingly the University Council of
Chulalongkorn University authorised the establishment of such a school on 3 January 1938. The founding of the school, which took place over a tight time frame of three months, was overseen by Mom Luang
Pin Malakul, then head of the university's teacher-preparation programme, who became the school's first director. The school took over the location of Mathayom Horwang School (of which ML Pin was also headmaster) on Phaya Thai Road in the vicinity of the university, and became known as the "University Preparatory School, Chulalongkorn University", or
Rong Rian Triam Udom Suksa Haeng Chulalongkorn Maha Witthayalai (). The school, which was the first
co-educational in the country, opened on 16 May 1938, and classes began on 19 May. The school rapidly grew over the first few years, admitting up to 568 students in the 1940 academic year. In December 1941, the school was occupied by Japanese forces
in the course of World War II, forcing the staff and students to relocate to temporary locations around Bangkok. Classes briefly returned to the school in 1943, but had to again leave after the school was damaged by Allied bombing on 19 January 1944. Part of the staff and students were transferred to various cities around the country, where preparations had already taken place for the establishment of additional preparatory school campuses. (Changes of government policy would however later cause these campuses to close down.) The school remained occupied even at the conclusion of the war, this time by Allied forces. Since the 1950s, the school staff have on multiple occasions been assigned by the Ministry of Education to assist other schools in staff training and teaching strategy development. In anticipation of the possible need to relocate in the 1970s, the school helped found the
Bodindecha and
Triam Udom Suksa Pattanakarn Schools in 1975 and 1978. Queen's College, Ratchaburi was established with like assistance in 1992. The school saw further expansion in the 1980s, partly due to the new national curriculum, and now had ninety classes. Several new buildings were built, and modern facilities were introduced, including the introduction of computer classes in 1992. The school received awards from the Department of General Education in 1982 and 1985, and the school library won awards in 1990 and 1991. Students featured prominently in national stages, and since 1990 have continuously won medals at the
International Science Olympiads. At present, Triam Udom Suksa School educates upper-secondary students in the
mathayom 4–6 levels. As of the 2017 academic year, there are 111 classes with 4,280 students and 219 teachers. ==Campus==