A major part of developing concept-based instruction is the use of an overarching idea to provide a conceptual lens through which students view the content of a particular subject. By using a conceptual lens to focus learning, students think at a much deeper level about the content and its facts (Erickson 2007). Therefore, the authors collaborated on an ecology unit with sixth graders that incorporated concept-based instruction into a problem-based activity. This article describes the steps they took to develop their concept-based unit. It also explains how students used their scientific skills of observing and inferring to explore and address an aerator problem in a pond ecosystem. (Contains 5 figures and 3 online resources.)