This simple inquiry-based lab was designed to teach the principle of osmosis while also providing an experience for students to use the skills and practices commonly found in science. Students first design their own experiment using very basic equipment and supplies, which generally results in mixed, but mostly poor, outcomes. Classroom “talk and argument” is then used to determine how their experiments could be changed to gather more reliable data. The final assessment consists of both formal and subjective testing, requiring students to explain their design choices.