We can thank Bush's "No Child Left Behind" for that. Around here, you can fail home school.
Reason I'm considered "failed" is because I only went for 3/4 of a year, and got switched to a new school, but they bumped me up mid-year to 1st grade, and so I never finished kindergarten. We never received the papers in the mail congratulating me for finishing a year of kindergarten, and the rules in any grade are, if you're in the class for over half of the year but don't finish, it's a fail.