shells (Either all the same type, or a variety--depending on the level of your students)
rulers
scales
1. Before students begin, write a number on each shell. (A dot of liquid paper on the shell is easier to write on than just the shell surface.)
2. Students choose a shell.
3. Students write a description of the shell they chose including size and weight. (Be sure they write the number of the shell on their paper. Students often forgot which shell they are describing.)
4. All shells are returned to the collection and the detectives are called.
5. The student reads the description and the detectives determine which shell is described.
(The first time we tried this, the children discovered they did not include enough information to be helpful to the detectives. Don't be surprised if they ask you to do this again. You will have must better observers the second time!)