Then why are there gaps in achievement by race?

is it a true gap by race, or gap by wealth?

and race is a confounding variable? I ask because I don't know.

If it is mostly economic, then I would posit that it is because children of more wealthy parents get more guidance and prep (both academic and test taking).

Not sure why in the case of race.

I don't know...the College Board doesn't capture those stats

That is, they capture race but not other socio-economic information from the test-takers.

I suppose my point is, on a truly standardized test (if such a thing exists), there ought not be differences by race, sex, or socio-economic class.

If it's a pure native talent test, that's true

However, it's hard to picture any test, however fashioned, whose outcome is unaffected by parental encouragement, school quality, nutrition, and other factors that are likely to be correlated with the variables which you mention.

this.

The SAT and ACT test intelligence, but also test academic achievement, and academic achievement is correlated to a certain extent with social circumstances of upbringing.

I'll sit here and wait for the pro-SAT crowd to respond. *