Middle Grade Series with Co-Authors:
* The Witch & Wizard Series (with Gabrielle Charbonnet):
* *The Witch & Wizard*
* *The Witch & Wizard: The Forbidden Game*
* *The Witch & Wizard: The Lost Colony*
* *The Witch & Wizard: The Final Battle*
* *The Witch & Wizard: The Lost City*
* *The Witch & Wizard: The Last Stand*
* *The Witch & Wizard: The Hidden Truth*
* Maximum Ride Series (with Andrew Neiderman):
* *Maximum Ride*
* *Maximum Ride: School's Out - Forever*
* *Maximum Ride: Saving the World and Other Extreme Sports*
* *Maximum Ride: Nevermore*
* *Maximum Ride: Angel*
* *Maximum Ride: Forever*
* *Maximum Ride: Fang*
* Daniel X Series (with Andrew Neiderman):
* *Daniel X*
* *Daniel X: The Second Time Around*
* *Daniel X: The Curious Case of the Killer K*
* *Daniel X: The Ultimate Power*
* The I Funny Series (with Chris Grabenstein):
* *I Funny*
* *I Funny: A Funny Thing Happened on the Way to the Middle School*
* *I Funny: The Big Laugh*
* *I Funny: The Worst-Case Scenario*
* *I Funny: The Totally True Story of the World's Greatest Liar*
Standalone Middle Grade Books with Co-Authors:
* *The House on the Hill* (with Chris Grabenstein)
* *The 100th Day of School* (with Chris Grabenstein)
* *Treasure Hunters* (with Chris Grabenstein)
* *The Perfect Present* (with Chris Grabenstein)
* *The Day You Begin* (with Jacqueline Woodson)
While these books are generally appropriate for middle school readers, it's always a good idea to check the age recommendations and reviews to ensure they're suitable for the specific child.