The school was founded by German-British educator
Kurt Hahn on 13 October 1963 with funding received from the
USAID,
Ford Foundation and donation of land by the Nigerian Western Regional government. Most of the founding teaching staff were British expatriate educators from
Gordonstoun in Scotland, which had also been founded by Hahn. The school is a
co-educational boarding and day School admitting pupils aged 10 to 16. It was primarily established for children of expatriates living and working in Nigeria. It opened its doors to children of expatriates of diverse nationalities, and highly placed Nigerians. The first Principal was David S. Snell (1963–1965), followed by John Gillespie(1965–1968). The longest-serving principal was Anglican clergyman Archdeacon J.A. Iluyomade (1969–1985). He was also the first indigenous head of the school. After him was Rev. (Dr.) Dapo Ajayi (1986–1988), then Dapo Fajembola (1990 –1991). Thereafter came the first female principal, Esther Adetola Smith (1991–2004). After her was R.O. Akintilebo (2006–2007), Dr. Mark Brai Malik (2007–2017), Phebean O. Olowe (2017–2022), Akintunde Yinka (since 2022) ISI runs social and extra-curricular activities such as the biannual international soiree, an evening where all the nationalities represented among staff and students display the food, clothing and other material aspects of culture for sale to raise money for the less-privileged, and the Charity walk. Academically, it originally followed the British system of five years to preparation for Ordinary Level (
General Certificate of Education) and
West African School Certificate Examinations, with another two years in the sixth form to prepare for Advanced level (General Certificate of Education) and Higher School Certificate examinations. As a result of the introduction of the 6-3-3-4 Nigerian educational system introduced in the late eighties, it runs the mandatory six years of secondary school education, in addition to preparing students for international exams like the annual
IGCSE 'O' Levels and Cambridge 'A' level exams. For many years, it has offered preparation for the
International Baccalaureate. Although it now follows the 6-3-3-4 system of Nigerian education, many of the students continue to prepare for international examinations. Dr. M.B. Malik worked assiduously as principal towards the resuscitation of the
Cambridge 'A' Level programme in September 2011, which continues. The School celebrated its golden jubilee in October 2013. ==Alumni==