Transitional books may, in fact, be chapter books, but chapter books which are liberally illustrated. One of the finest examples I've seen in recent days is Rosemary Wells' Lincoln and His Boys. Historically factual yet unswervingly human, the short and easy to follow chapters are punctuated by detailed full-color paintings (by P.J. Lynch, the talented artist behind The Christmas Miracle of Jonathan Toomey). The life of Lincoln and the terrible costs of the Civil War are skillfully interwoven as the years of Lincoln's election and presidency are viewed through the eyes of his sons (read an excerpt here). This is a apt choice for any classroom study of our 16th president, the Civil War, or the universal theme of perspectives (see a recent post on universal themes at my How to Teach a Novel blog).
Be sure to visit Candlewick for additional print and video resources and activities on some of your students' favorite books. My favorite: popular authors such as Kate DiCamillo discussing and reading from their upcoming books.