SAT mixes in intelligence with education so it's bound to skew more towards people with access, but it's also correlated with IQ, and IQ has significant heritab

SAT mixes in intelligence with education so it's bound to skew more towards people with access, but it's also correlated with IQ, and IQ has significant heritability as well (things like separated twin studies have shown the genetic component quite clearly). So it's probably a double whammy there - good environment and good genetics.