Since 2004, middle and high school students have been monitoring the effects of ground-level ozone by collecting data on observable leaf injury on cutleaf coneflower ("Rudbeckia laciniata") and crownbeard ("Verbesina occidentalis") in the Great Smoky Mountains National Park. This project is part of an ongoing citizen-science effort in which different groups of students assist researchers in tracking impacts throughout the growing season. Through this ozone-biomonitoring project, student participants gain understanding of the impacts of ground-level ozone on both plants and human health. In this article, the authors present an inquiry-based activity that follows the 5E learning cycle model. (Contains 8 figures and 9 online resources.)