Very interesting. I imagine an even simpler explanation for why poorer kids do less well in school:

You simply can’t focus on abstract thoughts if you’re lacking basic ingredients in your life.

It’s something like the pyramid of needs:

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When you’re hungry in school because you didn’t have proper breakfast because your parents had too little time to prepare one or were unable to actually buy proper-quality ingredients, your brain simply can’t focus on geography of the other end of the world or god forbid, calculus.

I guess that if schoolkids were given free meals before school and during midday break, their performance in school-related activity would improve by at least 50% in poorer regions.