The legal situation is the following:

The parent has to apply to the local school authorities before the school year in question to get the permission to "teach" at home. One has to follow the state curriculum, which is being tested at the end of the school year. If the child passes, one can reapply to homeschool in the following year. If the child fails, it has to resit the grade at a school, and most probably the family will be denied the possibility to homeschool in the future. In such a case, there is no legal way to repell.

So, although it’s entirely up to you how to acquire the knowledge, the content and pace of learning is strictly defined (in yearly steps). Which means quite a stretch to people who believe in natural learning.