Initially the younger students directly took classes while correspondence course were used for higher grade levels.
[6] In 1970 the ISOI board of directors decided to move the school to Islamabad, and in 1975 the current campus, located on a more than 23-acre (9.3 ha) site, and built with a large amount of U.S. government funding, opened.
In 1988 unarmed rocket-propelled grenades originating from an explosion of the Ojhri Camp ammunition depot landed on the school property.
The withdrawal of the United States Agency for International Development (USAID) from Pakistan caused a steady enrollment decline from 1992–1993 until 1997-1997, when the school had 555 students.
As a result, the U.S. government evacuated Americans from Pakistan, causing the ISOI enrollment to decrease to 510.