My daughter says she wants a book about sports, not romance, vampires, or fantasy. Basically, it's supposed to be middle school interests at middle school reading range. It seems that most books that are considered upper middle school reading are more about high school interests. Like boys or boys who are vampires or wizards. Since my daughter does not like boys, vampires, or wizards, she's kind of stuck with very few options.
In case you're looking to publish a book of your own that can be used with the AR test, the reading level is based on Flesch-Kincaid and then length of the novel. If you make it 100,000 words, for example, it will be exactly the reading level measured. That's about 400 pages. This article, by the way, with it's lack of multi-syllable words, is at a 6th grade reading level.