The school was founded by German-British educator Kurt Hahn[1] on 13 October 1963[2] with funding received from the USAID, Ford Foundation and donation of land by the Nigerian Western Regional government.

It opened its doors to children of expatriates of diverse nationalities, and highly placed Nigerians.

Akintilebo (2006–2007), M.B 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.

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.

Malik worked assiduously s principal towards the resuscitation of the Cambridge 'A' Level programme in September 2011, which continues.