Critically thinking about scientific data to form opinions on controversial issues in environmental health is crucial in undergraduate education in the field. An assignment paired with a "flipped" classroom activity was designed to impart knowledge on how to search the primary literature and extract data that can help formulate a point of view on several environmental topics including endangered species designation, genetic engineering, organic farming, population control, worldwide banning of DDT, mining/drilling, sushi, nationalized health care. Data are presented that show the assignment was effective in motivating critical thinking and making students take sides on these issues based on data rather than on values. This assignment is adaptable to any field of environmental science in which topics of controversy arise.