Reward systems are most effective when they're age-appropriate and geared towards the developmental level of the child. Toddlers and preschoolers are motivated effectively by simple sticker charts, while school-aged children do well with delayed rewards, such as a weekend trip to the zoo for earning two stickers each day during the week. Let older children earn privileges by accumulating points over a designated period of time.
When trying to motivate a toddler, focus the reward system on one behavior at a time, and choose a realistic, achievable goal. Place the sticker chart at the child's eye level in a prominent place, such as on the refrigerator or on the closet in his room. Let the child decorate the chart and choose his own stickers, and praise him liberally for his behavior each time he earns a sticker. This type of reward system is good for short-term goals like toilet training or motivating the child to sleep in his own bed.
School-aged children and preteens are able to delay gratification and grasp the concept that rewards must be earned. Tell the child that his privileges are contingent on his behavior, and set measurable goals that he needs to achieve. For example, if the child makes his bed three days in a row, he earns an extra hour of TV or video games. Use stickers, tokens, stars or any system that appeals to him to track his progress towards his goals.
By the time a child is a teenager, a behavioral contract usually is a more effective motivating tool than simple rewards. Make things such as spending time with friends, talking on the phone, borrowing the car or going to a party contingent on the teen completing his homework and his chores. Set clear guidelines. Be consistent, and remember that it's much more effective to grant privileges for good behavior than to punish bad behavior by taking them away.