Books are such a great way to expand vocabulary! We’ve been working our way through various series. Since it’s tricky to tell how advanced a book is simply by looking at it, I’ve put the ones we’ve used in approximate order of difficulty below. All links are to my reviews on this blog. This page is updated every time we try something new, so check back frequently!
Update: I just found another page that also categorizes books based on reading level. You may want to check that out as well: http://www.atelier.on.ca/edu/core.cfm?p=gradation.cfm&navID=gradation&L=2