Over the past year, educators have developed curricula teaching about the COVID-19 pandemic (Reed 2020; Royce 2020; Sadler et al. 2020). Many of these curricula feature computer simulations of epidemic dynamics (Kelter 2020; Sadler et al. 2020). Because an epidemic pattern is an emergent property of interacting human behaviors, it is crucial for students to recognize the mechanism of its emergence. This article describes an eight-day unit in which students develop their own epidemic simulations and use them to investigate how individual human behaviors and interactions give rise to the epidemic dynamics at the population level. NetLogo (Wilensky 1999), a beginner-friendly, agent-based computer modeling tool, is used to empower students to design and modify their simulations. They collect data, identify patterns, and use mathematical and computational thinking to understand infectious disease spread and control.