The Code
The universal SAT Home School Code, needed to register for the SAT and applicable anywhere in the USA, is 970000.
When you use this, it means that the score results will be sent directly to your home. Using this code simply indicates, for the sake of data gathering, that you are a home schooled student. Home schooled students, on average, score higher on the SAT than their public school counterparts. This code is the College Board's way of tracking the results accurately. Also, the SAT compares you to the local average, but as a home schooled student, you won't provide an accurate representation of the local district scores.
However, if you want to, you can use the local high school's code as well.