These are the instructions for setting up readability scores for Word 2013:
Open a Word doc.
On left side of toolbar RIGHT CLICK <FILE>.
Select <Customize the ribbon>.
Select <Proofing> on the left frame.
Select <Show readability stats>.
Now, when you perform <SPELLING AND GRAMMAR> on the REVIEW menu, you will receive a Flesch score, too.
There is likely this capability in earlier versions of Word, but you're on your own to figure it out.
