According to the linked article, social credit can be moved up or down for many reasons: "examples infractions include bad driving, smoking in non-smoking zones, buying too many video games and posting fake news online."

That means that if your social credit goes down for any of these reasons, which are not all financial, then you can be barred from the best schools.

I think it's far more likely to be used to keep top schools (which feed into top gov't/industrial positions) clean of any rabble-rousers.