I've been listening to Darwin's Origin of Species on audiobook, and I have a question...

Why is it that 9th grade biology is not completely dedicated to teaching evolution? Seriously, if evolution is the foundation of modern biology and medicine and genetics, etc., etc., why then is this not the focus of the biology curiculum? Surely, many other things can be taught along the way, but why is not at least one year dedicated to providing the evidence for supporting this foundational theory?

Is this not completely obvious?