So my son's school mailed out this new system for grading book levels called a "Lexile Measurement". It gives the reading level for the book and at what grade level you should be reading it. For example, Looking up Jim Butcher, he only has three books registered to date:
Storm Front - 830L
Fool Moon - 850L
Grave Peril - 730L
Now these numbers aren't directly correlary to grade level, but they do provide a wide range based on grade level. The breakdown can be found here:
http://www.lexile.com/about-lexile/grade-equivalent/grade-equivalent-chart/From the looks of the charts, these three books can start to be read from 4th grade (early) to 6th or 7th (ideal) and a bit further would be simple reading with few challenging words for the student.
If you're a published writer you need to speak with your publisher to get your book submitted to:
http://www.lexile.com. I'm not sure if there's a way a writer can have their own work graded officially. However, there's a nice tool that allows you to take a snippet of a book and have it tested here:
http://www.lexile.com/analyzer/ (You need to register to use it).
I see this serving three purposes:
1. It should help you find what books are within your child's reading capacity.
2. It should help you figure out what age level will be able to read your books. This can help with that whole "speaking to your audience" thing.
3. Someone tell Jim that he needs to kick his publishers in the butt to get the rest of his work graded. The Codex Alera series isn't even there.
If you already knew about this system forget I mentioned it. If you didn't, then, well, there you go. Go forth and check it out.