TBH, its EVEN more filtered than that. Zhongkao cuts out "dumb" kids. Migrant kids with wrong houkou can't drag down BSJZ scores, i.e. "dumb" kids get filtered

TBH, its EVEN more filtered than that. Zhongkao cuts out "dumb" kids. Migrant kids with wrong houkou can't drag down BSJZ scores, i.e. "dumb" kids get filtered out. But dumb is relative, IIRC PISA does ~10 Chinese provinces, even the shit tier ones that don't make BSJZ cuts had global average PISA 20 years ago, i.e. when those places were legit impoverished. Those provinced developed a lot since, their scores should regress towards tier1 mean - relative to growth a third tier city has more now than 1st tier 20 years ago. The main skew is like 20-30% of actually dumb kinds, because they got diverted to vocational, their education fine but less rigourous. Eitherway, hard to say, but look at proxy indicators, there's fuckload of "dumb" Chinese international students... i.e. those who couldn't hack GaoKao that are basically A students in western tertiary. And as others have mentioned, BSJZ + kids that pass zhongkao is basically more 2+ standard deviation talent pipeline than OCED combined, disproportionately directed at technical tertiary, i.e if you want to know who has most big brains whose going to be doing the cooking in the future, BSJZ is good indcator.