This paper reports on a study conducted to clarify issues involving reward effects in children's probability learning; specifically, the detrimental-effects-of-reward theory, and the utility and expectancy theories. Five event schedules in which the probabilistic versus partial reinforcement dimension was separated from the number of choices in the task were examined in a size discrimination task at two levels of reward (pennies and plastic token markers). The subjects were 100 fourth graders and 100 college students of both sexes. Whether or not the event probabilities summed to unity proved to be a significantly more important determiner of terminal performance than the number of response alternatives in the task. Females maximized significantly more than males and college students significantly more than fourth graders. Significantly greater maximization was also exhibited by fourth graders who were in the high reward condition. These reward effects appeared to be more consistent with a detrimental-effects-of-reward interpretation than either utility or expectancy interpretations. (Author/CM)