It sounds like your son and my daughter are about at the same math level. She is also 6 and she loves Cluefinder. It is her favorite computer game series. Recently, we purchased a 2 game package (3rd & 4th grade levels) at Best Buy for $20. It came with a set of fraction flashcards which led us to a discussion of reducing fractions.
I am also purchasing a subscription to Larson Math for my daughter to work on this summer. It is about $30/year. (much less than some of the other math curriculums). It is not as much fun as the computer games, but my daughter still enjoys using it. In addition, Larson Math is used at my daughter's school. I am hoping that she will be able to use it for math next year rather than doing 2nd grade math with her class.
Summer
