It can work, but it's not the ideal solution. I receive those who score high on their SAT's, aren't behavior problems, and can work independently. I have seperate reading and seatwork.
Tests are all at their grade level.
I do have difficulty with history, science, and health. Finding the time to do it is the main problem. My students have never complained about doing anything twice. I always tell them practice makes perfect. I guess they're satified with that.