In this study, 120 grade 9 high-ability students participated in a modelling activity in which they were facilitated by teachers in using a four-step problem-solving model (Polya, 1945) to elicit their own mathematics as they work the problem. The students were first presented with some statistical data from which they applied their mathematical knowledge to construct and analyse the models, used them to make prediction about future trends and evaluated their usefulness. In this process, the teachers structured the discussions by documenting students’ (1) understanding of the problem task, (2) plan of action, (3) carrying out the mathematical procedures, and (4) examining the solution with the assumptions made.