I find it unbelievable that "Shanghai" is allowed to stand for "China"--I know China is routinely allowed to get away with cheating and lying on all sorts of international competitions (sport comes to mind), but I would have expected more of PISA.
Like, OK, why don't we get to enter "London" and pretend it stands for the whole of the UK? Ridiculous.
And Shanghai standing for China is even more ridiculous than London standing for the UK.
As explained in the above link, China's restrictive internal migration policies tightly control who is allowed to qualify as a Shanhainese and take part in their education system.
I have travelled widely in China--the urban-rural gap is vast, and a huge % of Chinese children is very poorly educated and is struggling with other issues, like being dumped with barely literate grandparents who cannot take care of them properly, and the impact of soil and air pollution and undernutrition etc.