It was a delightful coincidence to read a unique picture book a few weeks ago, and later stumble upon a great writing activity to tie-in with the book. Mrs. Rojas posted this activity for students to stretch their imagination, which won't be hard at all once inspired by this engaging book: The Secret Knowledge of Grown-ups by David Wisniewski.
The book presents "top-secret" information about the hidden, previously undisclosed reasoning behind the rules adults enforce on kids. The book provides some truly fun, outlandish explanations for many of our rules (apparently, we tell kids to eat their vegetables not because they're healthy, but because vegetables will go on a rampage if we don't keep the upper-hand). The book is silly, and it kept students laughing.
Mrs. Rojas' activity includes a printable writing activity (I also found a similar one at writingfix) that asks students to imagine their own explanation for their parents' rules. You could adapt it to explanations for school rules. I imagine kids could come up with a ton of great reasons why we ask them to walk in quiet lines down hallways, or raise their hand to get permission to speak, or why they have homework. You could even have them illustrate pictures to go with their writing assignment.
Writingfix posted some nice examples of students' ideas. What ideas can your class create?