SOLVED. Middle Grade Coming of Age [s]

[Adina]

All the girls in my 5th grade class were assigned a novel in an attempt to help us talk more openly to each other about cliques/bullying/puberty... that I'm trying to locate again.

What I remember:
A young teenaged/pre-teen girl moves to a new town and starts school. On her first day she wears a polka dot dress that reminds people of the wonder bread logo and she's horribly embarrassed by the way they treat her.
There is some sort of mechanic whereby the students have an inside joke about certain colors of M&Ms meaning certain things.

I know it's not a lot to go on, but if anyone remembers this book I'd be really grateful, I've been wondering for years!

[Tab]

Wonder by Rachel Vail?

One of the reviews on goodreads mentions the girl being called "Wonder" after wearing a polka-dot dress.

If not:
How many years ago did you read this book?
Anything about the cover?
Part of a series?

[Adina]

That's exactly it. Thank you so much!