Pursuant to the 1971 U.S. Supreme Court case of Wisconsin v. Yoder, counties cannot force students to attend school after graduating from eighth grade. In this case the court held that Jonas Yoder's first amendment right to freedom of religion (the dude was Amish) outweighed the state's interest in educating the youth.
Stick that in your back pocket! Just another reason that the Amish rock. Late at night, when you're working hard on curriculum assigned to you after eighth grade, just think of Jonas and his first amendment rights...