Understanding human environmental health is difficult for high school students, as is the process of scientific investigation. This module provides a framework to address both concerns through an inquiry-based approach using a hypothesis-driven set of experiments that draws upon a real-life concern, environmental exposures to lead (Pb2+). Students learn how scientists use model organisms to understand basic biological concepts, and how these models relate to human and environmental health. Students observe how Pb2+ alters fish behaviors. Because many levels of biological organization are involved, this module has application for multiple units within general and advanced biology classes. Beginning with what is known about Pb2+ toxicity, students develop testable hypotheses about how it may affect behavior, apply this knowledge to human populations, and identify the "next experiment."