When I was a school, we had a simple merit / demerit system to help improve behaviour.
Each child in the school was a member of a house (I was Owls), and good deeds or work earned you merit points, bad behaviour earned demerits for the house total.
At the end of each term, the merits were added up for each house, then the demerits subtracted and the house with the most merits won the house cup – yes, a bit like Harry Potter.
Some classes had weekly or monthly prizes for the child with the most merits as well.