This two page (I recommend printing double sided) reflection sheet is a good written reflection for when students behave negatively. It has five questions with space for students to write answers.
There is also a spot at the end for a parent's signature. This allows parents to be made aware of any behavior issues before they become extreme.
I use this reflection as a step between the verbal warning and calling home. You can choose to use it at any point but I think it is most helpful before detention.