What if we had a page of all of the questions we ever got wrong sorted by earliest to latest. So we wouldn't have to go through all of the reviews and look at the right questions as well. And what if we could rate these problems personally (in terms of difficulty) in a separate category so we could know which questions we got wrong which were really hard and need review. One last thing, what if we had a little space on the questions to write a note to ourselves telling us what we did wrong. So for example, 

"Forgot tangents relation to sine and cosine"            or something like

"Forgot that numbers could be broken up into farther parts. So for example 4^2 could also be shown as 2^4."

And have all of these notes pop up in another category with the subject to the right of it.

I think these ideas could work not only for the SAT but for the other quizzes on Khan academy as well etc. I really love the Khan Academy SAT keep up the good work.