Hi Portia,
Our DD is further down this path. She is currently grade skipped one year and math accelerated an additional 3 (total of 4). When we were zooming through math just prior to starting public school to make sure DD hadn't skimmed too lightly, I found it helpful to buy the teachers edition of the math books that are used in our district. I bought the DVD/online version and they came with the full textbook and extensive recaps that summarized the learning goals for each chapter and section. (It was super helpful that our district used really ancient textbooks so buying them on EBAY was incredibly cheap ) This also gave me access to the tests for each chapter and year. Our deal was ace the chapter test and she didn't have to study it. If she didn't ace it, I had her read the learning goals and take the section test. It must be noted that she thought our district's textbooks were horribly dull, repetitive, and badly written. Four years later DD still mentions the publisher by name and credits their horribleness with "egging" her on to finish one more year of math so that she would not have to see them ever again (our district has other books for high school math).
Many people discouraged us from accelerating DD so rapidly in math and declared "What will she take after calculus? She'll run out of math in Sophomore year!" I'm happy to report that DD's school recently announced that they will have even more advanced International Baccalaureate math next year, so she will still not "run out of math". So I say "Go for it", let your son do math at the speed that makes him happy, but test him to make sure he has covered the curriculum and knows the district curriculum's vocabulary. Oh, and start looking ahead to plan for high school!
