This research examined whether the Siegler and Shrager (1984) model of strategy choice could be applied to a task and an age group quite different than those to which it had been applied previously. Earlier, the model had been applied to young children's arithmetic skills; here, it was applied to preadolescents' and early adolescents' performance on a balance scale task. The predictions of the strategy choice model regarding accuracy and solution times on several types of problems were contrasted with those of four other models. The pattern of results on the accuracy and solution time measures, as well as the children's explanations of their reasoning, were consistent with only one of the five models, the strategy choice model. The results were consistent with the view that the model can be used to characterize children's strategy choices whenever they possess both problem-specific associations and backup strategies. More generally, the results highlight the importance of problem-specific knowledge as part of the end point as well as the beginning point of many parts of cognitive development.