There is not one but two Chinas: one urbanized, mainly on the east coast, and rapidly growing in wealth; the other rural, in the interior of China or on the move as migrants, and mired in poverty. (As a rough proxy, recent population numbers put the Chinese rural share at 41%). PISA assesses achievement of the first China and ignores the second one.
The journal Science ran a 2017 feature story on Scott Rozelle, an economist at Stanford and director of the Rural Education Action Program (REAP). The project implements programs designed to improve health and education in rural China, also conducting research on the programs’ effectiveness. Over several years, REAP administered 19 surveys involving about 133,000 children in 10 poor provinces. The surveys revealed 27% of kids suffering from anemia, 33% with intestinal worms, and 20% struggling with uncorrected myopia.