My students have always had a high success rate with roots and affixes. One of the reasons is that I allow them to use real word parts to invent their own words... but only if they can back it up with a definition that makes sense when combining roots and prefixes!
For example, hypno = sleep, phil = love, and ist = someone who is or does something. If you put them together, you've got a hypnophilist! That's someone who loves sleep! Get it?
In this activity, students are supposed to invent different words that fit into certain categories(A superpower, an invention, a new medical condition or disease, etc.).
SPECIAL NOTE: A list of roots and affixes are NOT included with this product. I print out lists of roots and affixes from other websites. One cool thing that I also do is I use different colored index cards(Pink for roots, lime for suffixes, and orange for prefixes) and scatter the word parts all over the room. The kids have fun engaging themselves by going on "word hunts" while I can instantly see who is struggling with the concept and help them in real-time.