With the investigation into the black box concluded, the students had to design what they imagine could be the apparatus inside the black box. Using observation and experimentation the students had to use their data to help define the inner workings. Students discovered that when water was added, sometimes only a fraction of the water exited the box. Other times, the black box released more water than was added. Students had to make inferences about what would cause water in the box to behave in this manner.
Students had to defend their ideas in class by explaining how well their concepts matched the data collected during the investigation. The class discussed each team's ideas and helped them to make needed modifications.