New Zealand like other former British colonies has had an active cadet program, preparing secondary-age boys for military service. So far I have few details about the cadet program in New Zealand.
The uniforms involved have generally followed the uniforms of the New Zealand military. The boy pictured here was in school cadets about the time of World War I (1914-18). I am not sure if the boy pictured here wears short pants because the school uniform required shorts or because the New Zealand military uniform involved shorts. The British, New Zealand, and Australian soldiers during World War I and II, depending on theor posting, did wear shorts and kneesocks. I believe that this style first appered in British units stationed in India.
Related Links: Careful this will exit you from the Boys' Historical Clothing web site, but both sites are highly recommended
Apertures Press New Zealand book: New eBook on New Zealand schools
School Uniform Web SiteInformative review of British school uniforms with some excellent photographs
Boys' Preparatory Schools: Lovely photographic book on British Preparatory Schools during the 1980s with over 200 color and black and white images.