Mathvids.com provides free math videos for all levels of math from Middle school math through Discrete math. If your student is having trouble learning a concept from their math book, you can help them find the corresponding Mathvid video help them understand better.
You can also use the video as your own online textbook, following the videos and exercises in order. You would need to purchase a workbook or find worksheets to go with it though.
There are ads on these videos, but you can pay a reasonable subscription fee for an ad-less version. I don't mind looking at ipad commercials though. The paid subscription includes the ability to download videos for later use and the ability to make the videos full screen.
Advanced Algebra (II)
You will have to become a member (free) to use the site. Great for middle school, high school, and college.