In 1927 Canon Harold D. Littler, the Headmaster from 1919 to 1941, realised his ambitions when the school was acknowledged nationally as a public school.
In developing along such prestigious lines in the 1920s, the school acquired many of the trappings of a public school. These included a new house system, detailed uniforms, school honours, annual traditions such as Founder’s Day, encouragement for team sports and extra-curricular activities and, later, a cadet force.
A new residence for the Headmaster and the boarders, Red Barns, was purchased in 1920.
New playing fields followed and in 1932 the expanding school acquired a new laboratory, several new classrooms, and an impressive Great Hall, now Coatham Memorial Hall.
Academic standards were high, with the school producing a steady flow of university candidates as well the “best examination results in all England” on three occasions.
As before 1914, most pupils were local fee-payers, although in the 1930s the North Riding County Council provided increasing numbers of boys on scholarships, with pupil numbers approaching c.400 by 1939.
The War presented new challenges; Canon Littler retired to a parish in Warwickshire in 1941 and the new Headmaster, Robert W.G. Willis faced a demanding time, managing the over-crowded school amidst rationing, staff changes, and the daily pressures of a country at war.
Over 600 Old Coathamians served in the War and 54 who lost their lives were commemorated on a bronze memorial consecrated in 1948.