In the present study we analyze how students reason about or make inferences given a particular hypothesis testing problem (without having studied formal methods of statistical inference) when using Fathom. They use Fathom to create an empirical sampling distribution through computer simulation. It is found that most student´s reasoning rely on data and assimilate natural sampling variation, which are two fundamental ideas of inference. This result represents a significant change in their natural reasoning. An important misconception is believed Fathom simulates samples of the real population instead of a hypothetical one. [For complete proceedings, see ED581294.]