I place book pockets on the corner of each student's desk. Then I place a colored index card in the book pocket. I explain to them that this card is their own "credit card" (they can decorate it if they wish) Then as a see positive behavior in the class I hole punch the card. When the students obtain a certain amount of hole punches (you can determine the number) they can choose a small prize on Fridays and then it begins again on Monday. Just make sure only you have access to the hole puncher so it is not tempting for the "little ones" to be sneaky!