Ways to Improve SAT prep

One thing that is annoying for me is that I have a level 4 on everything in the whole Khan Academy reading and math and writing skills. But when I take a test I don't get a 1600, Khan academy instead of reducing the levels for the things I missed on a practice test leaves it as a level 4. I think the Khan academy should have a system where topics that you missed on a practice test drop in levels allowing you to know what to focus on then guess and hope it works.