Not going to school?

I've noticed something here that I've finally asked Auntie Miki about. One of Sakura's friends didn't go to school for a while. She just said she didn't want to go anymore and apparently her mom was okay with it. It was only after a week or two did the principal of the school get involved. It was almost three months before she went back to school! I asked Auntie Miki about it and she said that it's normal in most schools to have at least one student per grade not going to school and the parents can't say no to their kids so the kids miss school. The principal, if he's (she's) nice enough, he'll go to the student's house to find out why, but there is no agency or police that gets involved. So the student doesn't go to school for a while, the school will just try to get them back to school and there is no "holding back" of students in Japan, so the student will just go on to the next grade even though they missed a lot of class. I don't know the details about it, but the whole thing is just strange to me! What would happen to a student in the states if they just turned around and said "I'm not going to school anymore"?