An individual reward program sheet with goals set by students (I do it in conjunction with parents).
Students set goals and select their own rewards, this can be edited for each student.
At the end of each session/break, student meets with the teacher and together they decide whether or not their have achieved their goals. If the student has, they get a sticker/stamp in the box, if not, they miss out for that session.
A great visual way for students, teachers and parents to track difficult students behaviour.