In the first phase of this study an interdisciplinary curriculum unit was developed centered on the concept of sustainable development in tropical rainforests. The centerpiece of the interdisciplinary unit was the investigation of a simulated environmental problem which required students to develop and then decide on a solution, having weighed a spectrum of possibilities previously explored in class activities and discussions. In the second phase of the study, nine science teachers implemented the curriculum unit in their classrooms after attending a two-day training workshop. Teachers first administered environmental decision-making pretests to their students who had been randomly assigned in intact classes to experimental (interdisciplinary rainforest curriculum unit) and control (conventional curriculum) groups. On completion of the three-week unit, environmental decision-making posttests were completed by both experimental and control students. Inferential results implied that students exposed to the interdisciplinary curriculum unit offered more supporting statements for their environmental decisions as compared to control students. It was evident that females used more alternative reasoning categories than their male counterparts when reaching an environmental decision. These results support the use of interdisciplinary curricula for enriching the environmental decision-making of secondary students. (Author)