[happytoexplain]

But this is relative, right? We're talking about SATs vs just relying on grades. Do poor kids do worse on SATs relative to how they do in their class grades, as compared to other kids? I kind of just figured poor kids do worse overall.

[Jensson]

Its easier to get good grades in poor schools since regardless how you grade your teachers grade you against your peers, and poor schools have worse peers. So given same knowledge poor students have better grades, so their grades will be relatively better than their SATs.

At least in public schools were you don't have an incentive to give everyone an A, maybe private schools are different.