I LOVE to use contracts with students for a few reasons. First, they tend to take them very seriously especially when you ham it up, and say this is an "official" document. Secondly, they are GREAT to refer back to if the same student finds themselves in a similar situation for a second time. You can always say, "hey, you knew the consequences"! Lastly, it is a tangible item you can share with other staff members and families.
Check out the google doc of the Bullying Contract I made to hold students accountable for their actions when they find themselves involved in a bullying situation. The contract clearly outlines the actions that are not acceptable, and the consequences that will be given if the student demonstrates the aforementioned actions.
I always have the student fill out the contract as part of accepting responsibility for their actions. Once the contract is signed, I make copies to share with appropriate parties.
What are your thoughts on using contracts with students?