In recent years, many Taiwanese elementary schools have implemented extensive reading activities in their respective campuses. In order to motivate pupils to read, teachers and parents would offer pupils contingent rewards. As we know, the use of rewards in educational settings as a way to improve motivation is a controversial issue. Previous studies on rewards, mostly conducted in controlled situations, have recognized that the effects of a reward depend on the types of rewards used, the reward expectancy, the reward contingency, and the attributions made for receiving the reward. The purpose of this study is to realize the predictive model of rewards and identified the reward predictors for reading motivation. The survey participants were 722 pupils from five elementary schools in southern Taiwan. Using a longitudinal design, it collected pupils' reward experiences in extensive reading activities as well as their pre-reward and post-reward reading motivation. Simultaneous and longitudinal regression analyses indicated that the predictive model of rewards could explain the variances of intrinsic, extrinsic, and global reading motivation, even when including the effects of previous motivation. "Intangible rewards" and "effort attributions" positively predicted intrinsic reading motivation, extrinsic reading motivation, and global reading motivation; whereas "luck attribution" negatively predicted intrinsic reading motivation.