I went through early math like a breeze. Got it to 100%. and got it in my head "maybe this is too far back". So I tried a more advanced subject again. Again I was stumped. Then I went through his arithmetic track to 100%. I knew most of it but I also found my major flaws in a lot of my fundamentals of math. HUGE gaps. So I was flying through arithmetic and gaining knowledge now. Then something crazy happened that I wasn't aware that his site would do. It stopped letting me do mastery challenges when I got more then a couple problems wrong. It made me practice. Which at the time I thought was dumb. But then I did I practiced since I had nothing to do for the rest of the day and I didn't want to jump forward again. I learned a lot of concepts about even multiplication and division I wasn't aware of. I learned how to deal with fractions properly. But I felt this was all superficial. I thought ya sure I "knew" this and was just not getting into it. Soon later I mastered this section.
I then started on Pre-Algebra (this was a subject I always loved in school). It was going well and I got to the part on exponents and radicals. Then I started getting scared so I watched a video on negative exponents(a video i had watch awhile ago and it was baffling to me). I watched it and boom it clicked I knew what was going on I could solve this. And I worked through it and it was going well. Same thing with square roots, cube roots, lcm, GCD. They all seem fairly trivial now. I kept wondering "Why does this seem so tirvial now?"
So I sat and thought about this. All that practice on the fundamentals I had done recently had really taught me what I was missing. My roof wasn't leaking, my foundation was cracked and the ground water was coming through. I am not saying I am a master but I am saying that I have a lot more confidence in myself now and I am glad I swallowed my pride and went backwards to even lower math then my kids were doing.
So my TL:DR is go don't be afraid of looking stupid for going back to your foundation skills and fundamentals. If your having problems be honest with yourself and go back as far as you need to it will only help you in the long run.
I am having a ton of fun now and am looking forward to geometry, algebra, trig, calc, linear algebra. And I owe it all to Khan Academy. The way he structures it really forces you to learn even if you feel like maybe it is just letting you blow past. When I was doing early math. I could master 6 subjects from not practiced in one mastery challenge. Now at pre-algebra I am only able to go from "needs practice" to "level one" in a single mastery challenge. It is forcing me to go back and learn and take time. and missing a mastery challenge question really means something if I can't burn through it while also having my challenge locked out. It really does make it feel like a game. I hope anyone who is struggling with math will check out Khan Academy