Kriston-
You can administer an achievement test to your son right at home, with minimal cost. There are several different options, such as the WRAT, CAT5, and IOWA. My family uses the CAT just because it seems to address a wide array of skills for a relatively low investment. I believe we pay $40 per test, and we always order "up" a few years. I purchase the CAT through Family Learning Organization online, and the people there are very helpful and accommodating. Just FYI if you decide to go that route.
I have found the tests to be reassuring and also helpful in pointing out the occasional gap. For example, when one of my kids took the test normed for end of year kindergarteners, she scored in the 98th percentile overall, but we realized that she had no understanding of currency. We'd never thought to introduce her to coins and bills, and a kindergarten student is expected to know the various denominations and be able to count them a bit. We also learned through this same test that she could tell time at least to to the hour and half hour, although no effort had been made to teach her.
I do know unschoolers who don't do any testing and end up attending college and doing very well. It all depends upon what you are most comfortable with doing.
