Mary,
My DDs did Kumon a while ago but we stopped it. 1st- It is drill, drill, drill. A lot of repetition. My DDs dread over that. And it costs a lot of money as well. We were spending >$400 a month for Math and reading for 2 kids.
Singapore Math books are cheap and the kids can take it around. My DD8 did it for fun during school (when they are doing Math calsswork. I am sure your DS finish his before anyone else.)
There are a lot of online resources (some with a fee and some free) I like Khan academy. Your DS can progress on his own pace and there are plenty of video lectures as well.
