The Bahá'í summer schools were originated in America to meet the requirements of the friends. They have been adopted by other Bahá'í Communities the world over, but there is no reason why they should be called "summer schools". There is nothing rigid about the term, it is purely descriptive.
(From a letter dated 26 December 1941 written on behalf of Shoghi Effendi to the National Spiritual Assembly of Australia and New Zealand; The Compilation of Compilations vol. 1)