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I read that book in America, and I'm pretty sure the book was set in a vague, nameless place. I can't remember character names anymore, but I do remember almost everyone's secret that was stated:
- One girl used to be a swan.
- One boy loves his little sister instead of finding her annoying like everyone else.
- One boy's mother is the tooth fairy.
- One girl is allergic to secrets.
- The teacher sleeps in the school, and the classroom is actually her home, with the desks being her furniture.
- One boy wet his bed the night before school.
The book's general tone was humorous as well. This is one conversation I remember, though the specifics may be different.
"Hey, that's my house?"
"And is that your underwear your mom is hanging out to dry?"
"Um...let's keep going."
The Secrets of Ms. Snickle's Class. I remember reading this!
Here's the link:
http://www.amazon.com/Secrets-Ms-Snickles-Class/dp/0618034358/ref=sr_1_1?s=books&ie=UTF8&qid=1349634965&sr=1-1&keywords=secrets%2C+class

I read this book about 6-8 years ago, I believe, but since I borrowed it from the library it was probably older than that. It was basically about a class where all the students had secrets of some sort, and one of the students tries to figure out everyone's secret. I'm pretty sure the title was something like "The Secrets of [teacher name]'s Class." I actually remember a lot of detail about what everyone's secret was, but I'm hoping this is enough to go on.