Your teacher was wrong. I don't know how it's an "Oxford" comma or controversial at all. It just depends on what you're trying to say. For example:
"I dedicate this book to my parents, Ayn Rand and God."
So Ayn Rand and God are your parents, and you dedicate the book to them.
"I dedicate this book to my parents, Ayn Rand, and God."
So you dedicate the book to the following:
Both are completely correct grammatically, but they don't mean the same thing. As I mentioned the other day, commas save lives:
"Let's eat, grandma."
"Let's eat grandma."
Again, both of the examples are grammatically correct, but they don't mean the same thing. Taking out a necessary comma doesn't (always) make the sentence grammatically incorrect! It makes it mean something else.