This is a great introduction (or summative) lesson for prefixes. After having students learn the meaning of re and un I give them this sort. In pairs they create the headings (which I copy on colored paper) and then cut out the based words and put them under the correct heading. There is a worksheet that I use for them to fill out once they've sorted correctly that makes them think about the meaning of the words before and after adding the prefix.
My kids love the hands on / visual style of learning so this is a great activity for that.