My DD9 loves Khan Academy. It is slightly gamified and she really likes earning energy points and badges as she progresses through the lessons. Also, she is motivated to log in and learn something every day so she doesn't mess up her "streak".
I hadn't heard of Front Row before you mentioned it so I made myself an account and looked it over for a few minutes. I think Front Row looks specifically geared towards younger kids since it has a cartoon interface, with opportunities to earn stars and unlock later lessons. I think my daughter would like Front Row's kid-style interface better than Khan's.
Khan does a good job of adapting to DD's ability. If she gets a few problems correct, then the lesson is considered "mastered". If she doesn't, then she has to keep practicing it until she can do five problems in a row correctly. I did not have time to see how well Front Row does this same sort of adaptive learning. They do start out with a pre-test so the students start at the correct spot, but I'm not sure if it changes the number of problems assigned.
The biggest problem I see with Front Row is that it doesn't seem have nearly the depth or breadth of lessons that Khan academy does. Front Row ends at 8th grade. Khan goes all the way through differential equations and includes computer programing and science courses. I watched a video tutorial on comparing fractions on both sites and felt like the explanation on Khan was much more better.
Since no one else seems to have used both of them, I suggest you make accounts on both. Compare a few lessons, have your child try them out and then report back and let us know what you discover.
