After learning about the American Revolution on a family trip to Boston, Massachusetts, Judy Moody makes her own Declaration of Independence and tries to prove that she is responsible enough to have more freedoms, such as a higher allowance and her own bathroom.
Judy is excited about becoming a doctor, especially when Class 3T starts a new unit on the human body, but she learns more about being a patient when she catches tonsillitis from her little brother, Stink.
When her substitute teacher realizes she is struggling in math, Judy is sent to a math tutor at the local college and soon is completely into the spirit of college life.
When Judy Moody gets serious about protecting the environment, her little brother Stink thinks she is overdoing it, but she manages to inspire her third grade class to undertake an award-winning, environment-saving project.
Judy's big plans for the summer seem ruined when two of her best friends go away, and then her parents leave her and Stink with Aunt Opal, but a new "thrill-a-delic" plan has her racing toward fun.
Third grader Judy Moody is in a first day of school bad mood until she gets an assignment to create a collage all about herself and begins creating her masterpiece, the Me collage.