What a great way to illustrate to kids the meaning and importance of words. I recently read it again with my youngest son, and still loved it just as much.
In between, our family has read many of this author's wonderful books, all of which I would highly recommend. They are appropriate for middle grade readers (second grade and above could probably read most of them on their own) and they are innocent stories that teach a lesson without being sticky sweet or preachy.
Clements does have a YA series (at least one that I know of) which I've read the first two books: Things Not Seen (Penguin, 2004) and Things Hoped For (Penguin, 2008). The first is a favorite -- about 15 year old Bobby who wakes up one morning to find himself invisible. The joys and the perils of how he deals with this are fantastic. Especially when he finds the only one who can help him is a blind girl. The latest Things That Are (Penguin, 2008) came out last fall.
Other Clements favorites are No Talking (S&S 2007), The School Story (S&S 2002), and The Landry News (S&S 2000).
To learn more about the author, go to andrewclements.com.