HI Chris, Most of my published readers are aimed at teenagers - some comedy, some adventure, some romance. There tends to be a greater need for lower level material. For example, Richmond Readers started with levels, 1, 2, 3 and 4. Then teachers complained that the level 1 books were too difficult so we were asked to write 'starter level' books, using no past tense and very simple structures. That wasn't as tough as writing a 140 word story with just a 40 word vocabulary - which I recently did for Harcourt in the UK.
Have a look at www.jeremytaylor.eu
if you want to see the books and download some stories. I'll be putting more up later today.