This paper reports the findings of a qualitative study undertaken by the authors to investigate what students see when participating in a computer simulation session designed to support the development of conceptual understanding of the role of the sampling distribution in hypothesis testing. We have observed and documented the students' assisted interaction with a dynamic and interactive computer simulation, and looked for patterns and themes arising from the data. On the basis of the data collected, we have identified four developmental stages through which the students progressed during the activity, and we have termed these stages as recognition, integration, contradiction and explanation. The identification of the stages has given us some direction for the development of further computer interactions.