The history of Kowloon Junior School begins in 1900 when a donation of HK$15,000 was received from Mr Robert Hotung to pay for the cost of the building of a British School. A site was provided in the original Robinson Road, later to be renamed Nathan Road. In 1902, Kowloon British School was officially opened with 60 students. It was in 1923 when the school was renamed Central British School (now King George V School) to offer a secondary curriculum, and junior age children were relocated to the new Kowloon Junior School (KJS) on Gun Club Hill Barracks (now King’s Park). The number of students grew rapidly to 90. In 1929, KJS moved to Parkside opposite the Kowloon Cricket Club on Cox’s Road. However, during World War II, the building was destroyed. It was not until 1950 when KJS finally found its permanent home at Perth Street.

In 1980, KJS became an ESF school. In 1994, to meet the overwhelming demand for quality education in the community, KJS established extra classes at another school building on Rose Street. For the next 19 years, KJS had been existing on two separate sites until redevelopment of the new KJS campus was finally completed in August 2013, which now holds 900 children.