I have used this is my classroom for three years. It works like a charm. The students love to see how many gum balls they can earn during the given time. I have either set the timer for the full amount of work time or set it for smaller increments of time. As a reward, if they reach the goal, I sometimes give a piece of bubble gum, or something toward a classroom goal for some other reward...For example I might give them a letter toward building the word Compliments.