In their water unit, Grade 6 science students have been learning that clean freshwater water is not easy to find without treating it first. Because filtration is often the first stage of water treatment, students were challenged to design an effective water filtration system for clarifying dirty water. They were given a range of materials to choose from, including coffee filters, cotton balls, gravel, and sand. Success was measured by how well the dirty water passed through the filter without becoming clogged, and by the degree of clarity and transparency of their filtered water. After testing an initial prototype, they discussed the outcome, brainstormed improvements, and modified their filter to make it even more effective.