Hello Cory,
The reason Khan Academy is designed is to help students fill in the gaps and help students master skills.
I can see from your perspective when you have already master certain topics and subjects as you want to focus on your weaknesses and build your knowledge here are some basic things you can do to focus on faster learning.
1.Use Search bar for specific Terms and keywords this will direct you to where you truly need to study for your homework
2.Next scroll through subjects like Arithmetic and see the content that's broken down into smaller key concepts here you can decide what you truly need to study
3.Khan Academy has practice quizzes a new feature added you can quickly identify the areas you need to specifically study.

I hope these tips can help also if you have any questions I will be happy to help you.

Like I have a difficulty doing Graph from slope-intercept form and stuff like that I use you tube it can help me understand how to calculate Graph from slope-intercept form in depth, like step by step, even when you watch the Khan academy videos, I have been away from Khan academy for long It is about time I get back to things now. I left school because I was bullied had a hard time, I wanted to grow up I hated homework, computing and technology was my strongest points just the exact same way as Sal Khan said the way he became good at maths by playing around with things, that was exactly what I did with computers and technology now I'm a whiz at it but a bit rusty, I loved maths but I was never good at it the way I'm now, thanks to Khan academy I can do things I never knew I could no I'm at Graph from slope-intercept form level ugg but I will persevere is the key and never give up, now I look back to my school days and I say, I miss the tense drama lol I miss the homework, heck I miss the good old days, the point is be yourself, do what's comfortable to you and don`t listen to negativity directed to you, and stick to your homework and like Khan academy is doing you never know when you will need it, I miss school at much I can`t stop dreaming about it.