In this hands-on STEM challenge, 4th grade students work in pairs to design tin foil boats that can carry the most marbles before sinking. After predicting their vessel’s load capacity and recording key design choices, students observe as each boat is publicly tested in a fun, high-stakes “sink or float” showdown. Results are shared and analyzed as a class to uncover what makes an effective design. Throughout the activity, students engage in teamwork, measurement, data recording, and scientific