Khan Academy is a free online education program. They cover almost everything. Biology, physics, chemistry, history, economics, and math of all types, from one-digit addition to calculus.
I have been a member for over two years. Doodle has not even been a member for a year, but he is making amazing progress. He has won more awards than me and has almost as many points.
Khan Academy has courses on Canvas, a programming language designed for moving graphics. There are hundreds of amazing video games that have been created by students. It is the go-to place for computer games. The really cool part is that you can edit the code yourself, to customize the game to your preferences! Doodle is creating his own Canvas programs.
For homeschoolers, this is an great option because of its vast coverage and all the ways they make it interesting-- Doodle does this on his free time. He is very motivated about it; trying to get this award, or trying to master that skill, or trying to finish his canvas game.
There are some downsides.... they recently redid their site and started everybody's math status over again, and it didn't work out well. They had me take a test to see what level I was at, so that I wouldn't have to re-master simple arithmetic and things like that, but after the test they considered me not proficient in 2-digit addition! I am at a much higher academic level than Doodle is, but thus far according to them I have mastered 65 skills, and Doodle has mastered 165.
Also, Khan academy is like most non one-on-one education situations in the aspect that you're not forced to actually understand how it works, just how to get the answer right.