Making inferences is crucial for understanding the world. The school may develop such skills but there are few formal opportunities for that. This paper describes an experiment designed to investigate the use of qualitative reasoning models to support deaf students in making inferences about the behaviour of populations in interactions such as commensalism, amensalism, and predation. The experiment was done in two sessions. In both, the teacher presented the concepts, which were translated to the signed language, and at the end the students answer to a test, consisting of objective questions and a written essay. In the second session qualitative models about the interactions were used to show the structure of the two populations system and the dynamics of the system over time. Statistical analysis showed that the use of qualitative models had a significant positive effect on the performance of the students. They gave more correct answers to objective questions and produced less trivia...