HIES currently maintains formal sister-school relationships with high schools in Sapporo, Japan, Briey, France, Cape Town, South Africa, and Buenos Aires, Argentina.
The purpose of the HIES sister-school program is to promote cultural awareness and sensitivity, as well as to facilitate foreign language study where applicable. To this end, students hold regular videoconferences with their foreign counterparts, utilizing the latest web-based technology. Exchange trips also play a key role, with HIES students visiting their friends in their hometowns, and vice versa, every other year. During these trips, students stay with their counterparts' families, attend classes, and enjoy various cultural outings and events. Since the program's inception, a great number of close, personal relationships have blossomed between the students.