On this 3rd grade Homonyms worksheet, we added a "prize" that slowly appears as each wrong word is discovered.  When all the wrong words are found in each paragraph, the whole picture is shown. 

For this activity, just the fact the children recognize the wrong word is all that matters.  Although they must type the correct word in the box that appears, the "prize" doesn't depend on whether the correct word is used.

The text and pictures were first created in Microsoft Word.  It was then brought to Adobe Acrobat where the buttons and actions were added.