Rewards for Good Behavior

When I was telling Bryant goodbye this morning before I left for work, I noticed he had a sticker on his T-shirt. On the days he goes to the gym to work out, Allison gives him a sticker as a reward. Today she asked him if he planned to go, and when he said yes, she gave him his sticker in advance. (You wouldn't think stickers motivate adults, but he said he HAD to go to the gym today since she'd already given him a sticker.)