I've had a lot of difficulty with finding readiness as well. What I tried initially was Rightstart, but that petered out after awhile. So did Life of Fred because the story has "nothing to do with math". The only thing that took is Ed Zaccaro. We started with Primary Challenge Math and are now at Real World Algebra.
My son dislikes step by step instruction and prefers to "think" up the answer himself. He has a lot of holes in his instruction but seems to be picking them up as we go along. Sometimes, he flies through the material; other times, he needs more help. I bought Hands On Equation as a supplement for when he needs the extra help, but he prefers to use it sparingly. Your son sounds similarly impatient, so I thought our solution might be helpful to you.
