Could you be an Upstart Evidence Hunter?
The evidence for the educational and social value of a 'kindergarten stage' comes from a wide range of sources. Producing it has been a slow process of joining up dots between studies, surveys and different academic disciplines (and it's only been compiled because the Chair of Upstart happens to be writing a book on the subject!).
So far we've found no research studies specifically comparing practice and/or results in early-start and late-start countries – probably because, after a century of so of habit, every country takes its school starting age for granted. But there's bound to be much more evidence out there.
And new studies (like What it is all about: topic choices in young children's play by Hoyte, Degotardi and Torr, in International Journal of Children's Play, 2013) are appearing every day. So if you're browsing the internet and come across some, please get in touch via firstname.lastname@example.org Any new discoveries will, of course, be credited to the Upstarters who discover them!