Wow, she did great today.

Wow is what part of speech in the sentence?
I think a preposition but not sure?

3 answers

Nope. Look up interjections.
My ninth grade English teacher described prepositions as this: anything you can do with a stone in relation to a bolder: on, with, in, upon, beneath, of ...
Thanks!
It's not a preposition. Prepositions begin phrases.
Examples of prepositional phrases:
to the store
in a moment
from my friend
under the bed

Study this site.

http://www.chompchomp.com/terms/interjection.htm