To start with Welcome to our group!! You should become familiar with the laws in your state to begin with, assuming your still in KS you can find your state laws here:
HSLDA | Home School Laws. Depending on the curriculum you choose some have tests that you can go by. If you are really concerned you can do standarized tests to see where your child places. There are books out there called What Your Child Needs To Know By ...... (insert whatever grade) Grade. I havent really look at those before however, maybe someone here has. He will be fine, it is all about individual learning and if he ends up falling behind a little it is no big deal. If he struggles in an area there is no need to force the issue, you take the learning to his pace and if that means you spend more or less time on certain things then so be it. It all works out in the end :-)