We have studied what epistemic games students employ to formulate observations, hypotheses and design experiments within an investigative learning environment. The students participated in an activity based on ISLE (Investigative Science Learning Environment) focused on the melting of ice when some table salt is added to it. Two pairs of students were compared: a pair of engineering students and a pair of physics teacher students. Finally, two types of epistemic games were identified that made the physics teacher students more successful in their engagement with the activity than the engineering students.