The school originated as Belsize School, founded in 1889 by the Revd Francis John Wrottesley, who with his wife had taken fee-paying pupils at their home in nearby 18 Buckland Crescent since 1881. The Wrottesleys sold their school in 1898 to the Revd D. H. Marshall, who took over an adjoining house in 1903, when there were 58 boys, including 10 boarders. In 1905 Marshall bought the Allen Olney girls’ school, which his wife continued at Buckland Crescent.

Marshall moved the boys to Crossfield Road and renamed the school The Hall. The roll was over 100 in 1909, when he sold the school to G. H. Montauban. It prepared boys aged 5 to 13 for public schools and won many scholarships. Montauban bought Woodcote at 69 Belsize Park, at the corner of Buckland Crescent, in 1916 and opened it in 1917 for boys under 8. The school was recognized[clarification needed] from 1919, when Montauban sold The Hall to R. T. Gladstone, retaining the junior school until 1923.

In the 1920s the roll increased from 60 to 270. In 1935 ownership passed to a private company. The main building was extended in 1935 and the junior school in 1938. The roll fell to 45 in 1940, but under a new company rose to 170 in 1942. The junior school, evacuated in 1939, reopened in 1942 with 35 boys. The school became a charitable trust in 1952.

In 1951 there were 302 boys aged 5 to 15, including 30 boarders, but boarding ceased between 1967 and 1974. In 1983 the school prepared up to 320 boys for public schools.