The two main objectives of the present study were to get a better understanding of sixth-graders' solution processes with respect to arithmetic word problems and to investigate the possibility of improving children's problem-solving ability through instruction. As background for the study, a hypothetical model of the problem-solving process was developed based on previous research. In the first part of the investigation, quantitative and qualitative data on the forms of problem-solving behavior were collected in two classes. In this ascertaining study, important shortcomings in children's solution strategies were discovered, and it was hypothesized that these shortcomings could be overcome by instruction. Therefore a teaching experiment was undertaken during a two-week period involving teaching the experimental class a solution-strategy for word problems in which estimating the outcome of a problem was a central concern. Estimating a problem's outcome systematically before working out the solution was expected to be an effective heuristic strategy that induces pupils to analyze the problem on the one hand and to anticipate the solution on the other. At the end of the teaching program, a posttest was administered to the experimental and the control groups. The results of this experiment are discussed. (Author/MP)