We're using K12 and really like it. I wish we had used it from the start. The subscription is course by course, and when your child is ready to move up, you just contact them and ask them to switch out the courses. (You'll need to buy the books for the next course, but they're not too bad). Last spring, I had my then DS8 in four different grade levels, which is one of the reasons it worked so well for us. And it worked so well for me b/c it gave me a schedule, teaching plan and answers. On our own with an eclectic curriculum, we never seemed to do get through a day's work. I needed the organizational help. (Other curriculum we used last year pre-K12 - Michael Clay Thompson/Thomas?, Aleks, Life of Fred, local district social studies book, All About Spelling - that's a good one, CyberEd - he liked that one, too, Time4Learning - he loved that one).
You can get a 2 week demo from K12, but in the end, you should do what you're most comfortable with. good luck!
