Sal Khan has created a site that plays on kids desire / addiction to play video games :) and a parents desire to see their child actually learn and understand Math.
As they say on their site...
"With a library of over 2,600 videos covering everything from arithmetic to physics, finance, and history and 218 practice exercises, we're on a mission to help you learn what you want, when you want, at your own pace."
First thing I did was to set the kids up with student accounts which will track their progress and give levels of proficiency in each category of math. Then I made myself a coach account which allows me to keep track of both kids and how they were doing.
The exercises begin with very simple concepts. The kids would start at the first level solving equations. It took about ten problems for the site to determine if they were "proficient" at that concept or not and then the site would advance them to the next concept. The kids went through several levels very quickly as the site was basically assessing what their needs were. (Remind you we're talking about a 7th and 9th grader here) Happy kids: lots of levels, points gained, and trophies earned. Then that leveled off... slightly disappointed kids...and the real work and learning began.
What I like about the site: the kids learned what they needed to learn. Unlike a text book where you start at chapter 1 and work your way through... this site focuses on concepts, starting at basic levels and then progressing on only as the kids master the basics. My two older kids came out of the public system and their math education had holes everywhere. Khan has helped to fill in the holes, reinforced what needed shoring up, and refreshed what they already did know.
What I didn't like about the site: the "positive reinforcement bar" at the top of the page which would fill up as they successfully solved equations would empty at a disproportionate rate when they answered a question wrong. This led to very frustrated math students.
All in all though, Khan Academy really helped us this past year. We had no access to the next level of math text books that we would have needed and Khan Academy kept us going in Math. For that I am extremely grateful!