I teach first and fourth grade. First grade (most of them) doesn't really understand what a contract is, but they understand promises and keeping your word. So I switched to calling it Our Promise a couple of years ago. Usually all I have to do is point to where our promise is on the wall and remind them we said... and they usually correct their behavior. I call it "our promise" in 4th as well for consistency purposes.
I teach 1st Science and 4th Math. We make one chart for each grade. I write on sticky notes with a different color marker for each class. Then I go back later, remove the stickies, and write on the chart what we agreed upon. This year I titled my charts Our Science Promise and Our Math Promise. When I was in the traditional classroom, I just titled my chart Social Contract or Our Promise because I had the same students all day for every subject.
We have been in school for two and a half weeks, and I have students in all four classes reminding each other about our promise. It's a beautiful thing.