In this paper, we investigate students' use of the generate-and-test strategy to solve algebra word problems. This strategy involves first choosing an estimate for the answer and then checking whether the estimate satisfies the constraints of the problem. Based on verbal protocol data, we developed a production system model to simulate students' behavior when they apply this informal strategy. The model predicts problem features that should affect the difficulty of the problems. A large-scale experiment tested the predictions of the model. Verbal protocol data provided additional insights into how students use the generate-and-test strategy.
