If you’re going to teach pronunciation, you have to know how to pronounce it.
It’s one of the few English words that is exactly as it says on the tin. The “nun” is pronounced as “nun” or “none” and the “noun” in pronounce (the verb) is pronounced as “noun”.(ok reading that over, it’s not exactly clarifying the situation, is it? But as Feynman said, I’m explaining how it works, not why it’s like that- if you don’t like it find another universe.)
No, it’s not an American thing and no,it’s not an acceptable local regional non-standard.
https://english.stackexchange.com/questions/5732/why-is-the-spelling-of-pronounce-and-pronunciation-different
Click on the speaker button to hear it:
https://www.macmillandictionary.com/dictionary/british/pronounce