Going by memory, the Ramona books are 4th-5th grade level in Accelerated Reader (what our school uses), and Judy Moody is 2nd-3rd grade. So the books each kid is reading seems commensurate with the perceived reading level to me.
Our school uses STAR to assess reading ability by test (rather than by what the kids actually read), and in my experience, it greatly over-estimated DD's reading ability. Although once you get over 6th grade, it's hard to find stuff that will hold a younger kid's interest, or books that don't have an intimidating thickness or density of words on the page. (DD has become a fan of Kindle books, because you can make the words less dense.)
