We propose a reward system that would reward each student for each day they are drug free.
For example each student would get a star sticker each day they are drug free and after so many days they can redeem their stickers for a real reward. Like gift cards.
Once the student hits a milestone such as 100 days drug free there can be a better reward such as a larger amount gift card or perhaps a day off from school. These milestone could be after 50 days, 100 days, 250 day 500 and so on.