This study investigated a theoretical structure which attempts to explain the problem-solving strategies used by first-grade students who are successful in solving simple arithmetic story problems. The structure used describes the problem-solving procedure as consisting of a three-stage model building process: (1) comprehending the story, (2) building a general conceptual model, and (3) generating a mathematical model. Results, based on a study of the performance of 81 students, appear to support the proposed theoretical structure in that essentially all students who can give the correct answer to a problem are able to develop a general model of the problem. (Author)