This study investigated changes in students' cognitive reasoning as they analyzed the dynamics of a rainforest ecosystem (El Yunque) in the aftermath of a hurricane in Puerto Rico. Students explore the virtual rainforest to study what happened to a type of frog after the hurricane. The culminating event is a simulation in which students manipulate the environmental conditions to recreate the dynamics of the frog population after the hurricane. Subjects were 54 students from a sixth grade class. Students answered reflective questions at the end of each activity, and their responses were coded to indicate the levels of cognitive reasoning shown. A main effect for project phase was found, indicating that there is a statistically significant difference between students' levels of cognitive reasoning at each phase. Student responses after using the simulation contained the highest level of student cognitive reasoning. This finding points to the possibility of using dynamic simulations in situations where the underlying concept is itself dynamic. (Contains 1 table and 15 references.) (SLD)